diff --git a/README.md b/README.md
index a4b2a16..61b44aa 100644
--- a/README.md
+++ b/README.md
@@ -41,7 +41,7 @@ are regenerated on each release — patches cannot be merged directly.
 Report problems (or send patches) to the author; accepted changes are
 applied to the development tree and appear in a following snapshot.
 
-This snapshot was assembled from development commit `15b822f06ee0`.
+This snapshot was assembled from development commit `64b1abf23e56`.
 
 ## License
 
diff --git a/com/kdesc.cpp b/com/kdesc.cpp
index 0168177..9ee660b 100644
--- a/com/kdesc.cpp
+++ b/com/kdesc.cpp
@@ -5,7 +5,8 @@
 #include "font_store.h"
 #include "ktype.h"
 #include "log.h"
-#include "argtype_set.h"
+#include "argtype_registry.h"
+#include "klammerset_registry.h"
 #include "character.h"
 #include "show.h"
 #include "util.h"
@@ -32,6 +33,37 @@ static void font_usage()
         "and then in the default font set.\n";
 }
 
+static void klammerset_usage()
+{
+    std::cout <<
+        "Klammerset commands:\n"
+        "  --klammerset                  List the klammersets on the search path\n"
+        "  --klammerset list             The same\n"
+        "  --klammerset help             This description\n"
+        "\n"
+        "A klammerset symbol x names the declaration file x/x.k, searched for in:\n"
+        "the current directory (for ktext, the input document's directory), the\n"
+        "KLAMMERTEXT_KLAMMERSETS directories (colon-separated; default\n"
+        "$HOME/.klammertext/klammersets), and $KLAMMERTEXT_HOME.  The first hit\n"
+        "wins, so a document-local klammerset shadows an installed one, which\n"
+        "shadows a distributed one.\n";
+}
+
+static void klammerset_command(const strings_t& words)
+{
+    std::string verb = words.empty() ? "list" : words[0];
+    if (verb == "list") {
+        std::cout << boldblack << "Klammersets\n" << black
+                  << describe_klammerset_search(fs::current_path().string());
+    } else if (verb == "help") {
+        klammerset_usage();
+    } else {
+        std::cout << "Unrecognized klammerset command: --klammerset "
+                  << join(words, " ") << "\n\n";
+        klammerset_usage();
+    }
+}
+
 static void font_command(const strings_t& words)
 {
     std::string verb = words.empty() ? "list" : words[0];
@@ -70,13 +102,14 @@ int main(int argc, char* argv[])
         args.flag("targets", "Show targets defined by the input file");
         args.flag("klammers", "Show klammers defined by the input file");
         args.var("font", "List installed fonts.  Enter \"--font help\" for font maintenance commands.");
+        args.var("klammerset", "List the klammersets on the search path.  Enter \"--klammerset help\" for details.");
         args.opt("v",  "'verbosity'", "n", "0", "'verbosity'");
 
         if (show_usage(argc, argv)) {
             args.usage(file_basename(argv[0]));
             exit(1);
         }
-        auto p = [&](std::string name) { return args.get(name) == "true"; };
+        auto p = [&](const std::string& name) { return args.get(name) == "true"; };
 
         args.parse(argc, argv);
         verbose_level = stoi(args.get("v"));
@@ -90,7 +123,7 @@ int main(int argc, char* argv[])
         }
 
         if (p("a")) {
-            Argtype_set argtypes;
+            Argtype_registry argtypes;
             std::cout << boldblack << "\nStandard klammer argument types\n" << black;
             std::cout << argtypes.describe() << "\n";
         }
@@ -116,6 +149,19 @@ int main(int argc, char* argv[])
             return 0;
         }
 
+        // The --klammerset subcommands operate on the search path
+        // (filesystem enumeration) and load no klammer set.
+        if (args.given("klammerset")) {
+            strings_t words {};
+            for (const std::string& w : args.as_vector("klammerset")) {
+                if (!w.empty()) {
+                    words.push_back(w);
+                }
+            }
+            klammerset_command(words);
+            return 0;
+        }
+
         Machine M;
 
         strings_t input_filenames = resolve_filename_list(args.get("input"));
@@ -124,6 +170,13 @@ int main(int argc, char* argv[])
             M.read(fs::path(M.m_state.value("KLAMMERTEXT_HOME") + "/sks/sks.k"));
         } else {
             for (auto fname : input_filenames) {
+                if (is_klammerset_symbol(fname)) {
+                    // A bare symbol resolves on the klammerset search
+                    // path; kdesc has no input document, so the local
+                    // stage is the cwd.
+                    fname = resolve_klammerset_symbol(
+                        fname, fs::current_path().string(), Locator()).string();
+                }
                 std::cout << "Read " << fname << "\n";
                 M.read(fs::path(absolute_pathname(fname)));
             }
diff --git a/com/kdiag.cpp b/com/kdiag.cpp
index 6c87a83..5642380 100644
--- a/com/kdiag.cpp
+++ b/com/kdiag.cpp
@@ -45,7 +45,7 @@ int main(int argc, char* argv[])
             args.usage(file_basename(argv[0]));
             exit(1);
         }
-        auto p = [&](std::string name) { return args.get(name) == "true"; };
+        auto p = [&](const std::string& name) { return args.get(name) == "true"; };
 
         args.parse(argc, argv);
         verbose_level = args.as_int("v");
diff --git a/com/ktext.cpp b/com/ktext.cpp
index c361865..62e81bd 100644
--- a/com/ktext.cpp
+++ b/com/ktext.cpp
@@ -7,7 +7,8 @@
 #include "util.h"
 #include "machine.h"
 #include "show.h"
-#include "target_set.h"
+#include "target_registry.h"
+#include "klammerset_registry.h"
                 
 int main(int argc, char* argv[])
 {
@@ -17,10 +18,10 @@ int main(int argc, char* argv[])
         args.req("filenames", "Input files in Klammertext format. ", "'list'");
         args.opt("s", "Text processed before input files.", "input-string", "", "'text'");
         args.opt("t","Output target; default is general (unspecified)", "target",
-                 Target_set::general_name, "'word'");
+                 Target_registry::general_name, "'word'");
         args.opt("o", "Output basename; meaning and default defined by target.", "basename",
                  "", "'word'");
-        args.opt("k", "File containing the klammerset definition; default is the Standard Klammer Set. With a value of \"none\", no klammerset is loaded.",
+        args.opt("k", "Klammerset symbol (resolved on the klammerset search path) or the pathname of a klammerset definition file; default is the Standard Klammer Set. With a value of \"none\", no klammerset is loaded.",
                  "pathname", "", "'word'");
         args.flag("d", "Display the output to the screen, rather than writing files.");
         args.flag("m", "Show the Klammermachine state at the beginning of processing.");
@@ -83,6 +84,12 @@ int main(int argc, char* argv[])
         if (klammerset_filename != "none") {
             if (klammerset_filename.empty()) {
                 klammerset_filename = M.m_state.value("KLAMMERTEXT_HOME") + "/sks/sks.k";
+            } else if (is_klammerset_symbol(klammerset_filename)) {
+                // A bare symbol resolves on the klammerset search path;
+                // the local stage is the input document's directory (the
+                // cwd when the input is a string).
+                klammerset_filename = resolve_klammerset_symbol(
+                    klammerset_filename, M.m_state.value("K_input_dir"), Locator()).string();
             }
             K::log(1, "Reading klammerset filename: "  + klammerset_filename);
             M.read(fs::path(klammerset_filename));
diff --git a/doc/edit/sublime/README.md b/doc/edit/sublime/README.md
index ef6b26c..72f8217 100644
--- a/doc/edit/sublime/README.md
+++ b/doc/edit/sublime/README.md
@@ -151,6 +151,35 @@ in the package folder (its name is shown at **Preferences ￫ Settings** under
 `color_scheme`), choosing a light or dark source file to match the ground.  The
 exact values are in each file's header comment.
 
+## Sublime Merge
+
+Sublime Merge reads the same `Packages` directory as Sublime Text, so the
+package installed above needs no separate installation: `.kt` and `.k` files
+are syntax-highlighted in Merge's diffs, and an edit to the syntax file is
+picked up live, exactly as in the editor.
+
+Only the syntax file crosses over.  Merge has no Python plugin host — it
+ships no `plugin_host` binary — so none of this package's code runs there:
+
+| File | In Sublime Merge |
+|------|------------------|
+| `Klammertext.sublime-syntax` | Works.  Delimiters and removed text are colored in diffs. |
+| `Klammertext.py`, `Klammertext_indent.py`, `Klammertext_align.py` | Do not run: no plugin host. |
+| `Default.sublime-keymap` | Inactive — it binds plugin commands. |
+| `Comments.tmPreferences` | Inactive — Merge does not edit text. |
+| `Breakers` / `Celeste` / `Mariana` / `Monokai` / `Sixteen` `.sublime-color-scheme` | Not used.  They override Sublime Text's built-in schemes by name; Merge has its own. |
+
+So delimiter matching — **Ctrl+M** and the live highlight of the matching
+delimiter — is a Sublime Text feature only.  Merge colors the delimiters but
+cannot match them: matching is context-sensitive code, not a syntax rule
+(which is why it is a plugin in the first place).  Merge's built-in bracket
+matching does not stand in for it either; that matches literal `(`, `[`, `{`
+characters, not `@name ... name@` runs.
+
+Merge colors the Klammertext scopes with its own scheme, so the hues differ
+from the editor's — the token classes are distinguished, but the package's
+five color schemes do not apply.
+
 ## Keeping literal klammers in sync
 
 Klammers whose content is verbatim (`@code ... code@`) are listed in the
diff --git a/mac/Makefile b/mac/Makefile
index 59ec1fa..7c93fa4 100644
--- a/mac/Makefile
+++ b/mac/Makefile
@@ -8,9 +8,9 @@ include $(K)/env/makefile.env
 
 # Source files
 BASENAMES := util error locator file argv character ktype katom katom_list \
-             log show command argument argument_set argtype argtype_set \
-             state eval eval_python eval_cpp klammer klammer_set deftype \
-             target target_set machine font_store
+             log show command argument argument_set argtype argtype_registry \
+             state eval eval_python eval_cpp klammer klammer_registry klammerset klammerset_registry deftype \
+             target target_registry machine font_store
 
 SOURCES := $(addsuffix .cpp,$(BASENAMES))
 OBJECTS := $(addsuffix .o,$(BASENAMES))
diff --git a/mac/argtype.cpp b/mac/argtype.cpp
index 877e373..632480b 100644
--- a/mac/argtype.cpp
+++ b/mac/argtype.cpp
@@ -6,9 +6,10 @@
 #include "error.h"
 #include "util.h"
 
-Argtype::Argtype(std::string name, std::string desc, std::string symbolic_pattern, std::string pattern,
-                 std::string default_value, std::string alone_value,
-                 std::string python_cast, modify_string_f python_format,
+Argtype::Argtype(const std::string& name, const std::string& desc, const std::string& symbolic_pattern,
+                 const std::string& pattern,
+                 const std::string& default_value, const std::string& alone_value,
+                 const std::string& python_cast, const modify_string_f& python_format,
                  const Locator& loc)
     : m_name(name)
     , m_desc(desc)
diff --git a/mac/argtype.h b/mac/argtype.h
index 00e5913..9f850fd 100644
--- a/mac/argtype.h
+++ b/mac/argtype.h
@@ -25,9 +25,10 @@ public:
         , m_loc()
         {};
 
-    Argtype(std::string name, std::string desc, std::string symbolic_pattern, std::string pattern,
-            std::string default_value, std::string alone_value,
-            std::string python_cast, modify_string_f python_format,
+    Argtype(const std::string& name, const std::string& desc, const std::string& symbolic_pattern,
+            const std::string& pattern,
+            const std::string& default_value, const std::string& alone_value,
+            const std::string& python_cast, const modify_string_f& python_format,
             const Locator& loc);
 
     std::string python_value(const std::string& var_name, std::vector<std::string> value, size_t name_size);
diff --git a/mac/argtype_set.cpp b/mac/argtype_registry.cpp
similarity index 90%
rename from mac/argtype_set.cpp
rename to mac/argtype_registry.cpp
index 71d0afd..d90ec39 100644
--- a/mac/argtype_set.cpp
+++ b/mac/argtype_registry.cpp
@@ -3,7 +3,7 @@
 #include <algorithm>
 #include <numeric>
 
-#include "argtype_set.h"
+#include "argtype_registry.h"
 #include "error.h"
 #include "show.h"
 #include "log.h"
@@ -11,13 +11,13 @@
 #include "character.h"
 #include "katom.h"
 
-Parameter_set& Argtype_set::parameters()
+Parameter_set& Argtype_registry::parameters()
 {
     static Parameter_set instance("name | desc :pattern .* :python_cast str :default :alone");
     return instance;
 }
 
-Argtype_set::Argtype_set()
+Argtype_registry::Argtype_registry()
 {
     (void)(void)K::log(2);
     Locator loc = current_locator();
@@ -33,7 +33,7 @@ Argtype_set::Argtype_set()
     m_types["bool"].m_alone = "true";
 }
 
-std::string Argtype_set::replace_symbols(const std::string& pattern, const Locator& loc)
+std::string Argtype_registry::replace_symbols(const std::string& pattern, const Locator& loc)
 {
     std::smatch match {};
     std::regex symbol_pat(R"('(\w+)')");
@@ -54,7 +54,7 @@ std::string Argtype_set::replace_symbols(const std::string& pattern, const Locat
     return expanded;
 }
 
-void Argtype_set::check_for_existing_definition(
+void Argtype_registry::check_for_existing_definition(
     const std::string& name, const Locator& loc)
 {
     if (count(m_names.begin(), m_names.end(), name) > 0) {
@@ -65,7 +65,7 @@ void Argtype_set::check_for_existing_definition(
     }
 }
 
-void Argtype_set::add(const std::string& name, const std::string& desc,
+void Argtype_registry::add(const std::string& name, const std::string& desc,
                       const std::string& pattern, const std::string& default_value,
                       const std::string& alone_value,
                       const std::string& python_cast, modify_string_f python_format,
@@ -130,15 +130,15 @@ void Argtype_set::add(const std::string& name, const std::string& desc,
     m_names.push_back(name);
 }
 
-void Argtype_set::add(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms)
+void Argtype_registry::add(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms)
 {
     (void)K::log(3);
     auto [positional, optional, rest] =
-        argument_split(begin + 1, end - 1); //, Argtype_set::parameters.m_positional.size());
+        argument_split(begin + 1, end - 1); //, Argtype_registry::parameters.m_positional.size());
 
     check_for_existing_definition(positional[0][0].m_text, begin->m_loc);
 
-    auto values = Argtype_set::parameters().value_map(positional, optional, rest, begin->m_loc);
+    auto values = Argtype_registry::parameters().value_map(positional, optional, rest, begin->m_loc);
 
     // std::for_each(begin, end+1, [](Katom& k) { k.m_type = katom_t::replaced; });
 
@@ -151,7 +151,7 @@ void Argtype_set::add(std::vector<Katom>::iterator begin, std::vector<Katom>::it
     ignore_whitespace(next_iter, katoms);
 }
 
-Argtype Argtype_set::get(const std::string& name, const Locator& loc) const
+Argtype Argtype_registry::get(const std::string& name, const Locator& loc) const
 {
     if (is_not_in(name, m_names)) {
         std::stringstream msg {};
@@ -162,7 +162,7 @@ Argtype Argtype_set::get(const std::string& name, const Locator& loc) const
 }
 
 
-std::string Argtype_set::eval(
+std::string Argtype_registry::eval(
     const std::string& value, const std::string& type_name, const Locator& loc)
 {
     std::regex re = m_types[type_name].m_regex;
@@ -193,7 +193,7 @@ static std::string values_note(const Argtype& type)
     return note.str();
 }
 
-std::string Argtype_set::describe(bool long_form, int indent_width) const
+std::string Argtype_registry::describe(bool long_form, int indent_width) const
 {
     std::string indent(' ', indent_width);
     std::size_t name_width = std::accumulate(
diff --git a/mac/argtype_set.h b/mac/argtype_registry.h
similarity index 96%
rename from mac/argtype_set.h
rename to mac/argtype_registry.h
index 95954e9..777f28e 100644
--- a/mac/argtype_set.h
+++ b/mac/argtype_registry.h
@@ -8,12 +8,12 @@
 #include "katom.h"
 #include "argument_set.h"
 
-class Argtype_set
+class Argtype_registry
 {
 public:
     static Parameter_set& parameters();
 
-    Argtype_set();
+    Argtype_registry();
 
     std::string replace_symbols(const std::string& pattern, const Locator& loc);
     void check_for_existing_definition(const std::string& name, const Locator& loc);
@@ -29,7 +29,7 @@ public:
     std::string eval(const std::string& value, const std::string& type_name, const Locator& loc);
     std::string describe(bool long_form=false, int indent_width=4) const;
 
-    inline bool is_defined(std::string name) {
+    inline bool is_defined(const std::string& name) const {
         return count(m_names.begin(), m_names.end(), name) > 0;
     }
     std::vector<std::string> m_names {};
diff --git a/mac/argument.cpp b/mac/argument.cpp
index 6d964ed..3f730e6 100644
--- a/mac/argument.cpp
+++ b/mac/argument.cpp
@@ -1,8 +1,8 @@
 #include "argument.h"
 #include "argtype.h"
 
-Parameter::Parameter(const std::string& name, Argtype argtype, const Locator& loc,
-                   bool optional, std::string default_value)
+Parameter::Parameter(const std::string& name, const Argtype& argtype, const Locator& loc,
+                   bool optional, const std::string& default_value)
     : m_name(name)
     , m_argtype(argtype)
     , m_optional(optional)
diff --git a/mac/argument.h b/mac/argument.h
index 2fb5b9c..335f409 100644
--- a/mac/argument.h
+++ b/mac/argument.h
@@ -19,11 +19,10 @@ public:
         , m_target()
         {};
 
-    Parameter(const std::string& name, Argtype argtype, const Locator& loc,
-             bool optional=false, std::string default_value = "");
+    Parameter(const std::string& name, const Argtype& argtype, const Locator& loc,
+             bool optional=false, const std::string& default_value = "");
     ~Parameter() = default;
 
-    std::string python_value(std::string value);
     bool undefined() const { return m_name == "_default"; };
 
     std::string m_name {};
diff --git a/mac/argument_set.cpp b/mac/argument_set.cpp
index 7d39234..a20a3b9 100644
--- a/mac/argument_set.cpp
+++ b/mac/argument_set.cpp
@@ -5,7 +5,7 @@
 #include "show.h"
 #include "log.h"
 #include "katom.h"
-#include "argtype_set.h"
+#include "argtype_registry.h"
 #include "argument_set.h"
 #include "util.h"
 
@@ -36,7 +36,7 @@ std::regex parameter_regex(bool optional=false)
 // rest(2): the base type is copied, its type parameter set, and its
 // display name extended, so kdesc signatures show rows.rest(2).
 static Argtype resolve_argtype(
-    const std::string& type_text, const Argtype_set& argtypes, const Locator& loc)
+    const std::string& type_text, const Argtype_registry& argtypes, const Locator& loc)
 {
     static const std::regex parameterized(R"((\w+)\((\d+)\))");
     std::smatch match {};
@@ -58,7 +58,7 @@ static bool is_rest(const Argtype& argtype)
 Parameter_set::Parameter_set(const std::string parameter_string)
 {
     (void)K::log(3);
-    Argtype_set argtypes {};
+    Argtype_registry argtypes {};
     parse_parameters(
         katomize(line_split(parameter_string), Locator().str()),
         argtypes);
@@ -69,11 +69,11 @@ Parameter_set::Parameter_set(const std::vector<Katom>& katoms)
         : m_katoms(katoms)
 {
     (void)K::log(3);
-    Argtype_set argtypes {};
+    Argtype_registry argtypes {};
     parse_parameters(m_katoms, argtypes);
 }
 
-Parameter_set::Parameter_set(const std::vector<Katom>& katoms, const Argtype_set& argtypes)
+Parameter_set::Parameter_set(const std::vector<Katom>& katoms, const Argtype_registry& argtypes)
         : m_katoms(katoms)
 {
     (void)K::log(3);
@@ -82,7 +82,7 @@ Parameter_set::Parameter_set(const std::vector<Katom>& katoms, const Argtype_set
 
 // Parameter parsing
 
-Parameter parse_positional_parameter(const katom_list& katoms, const Argtype_set& argtypes)
+Parameter parse_positional_parameter(const katom_list& katoms, const Argtype_registry& argtypes)
 {
     // (void)K::log(3, katoms);
     if (katoms.size() > 1) {
@@ -110,7 +110,7 @@ Parameter parse_positional_parameter(const katom_list& katoms, const Argtype_set
 }
 
 
-Parameter parse_optional_parameter(const katom_list& katoms, const Argtype_set& argtypes)
+Parameter parse_optional_parameter(const katom_list& katoms, const Argtype_registry& argtypes)
 {
     //(void)K::log(3);
     Katom k = katoms[0];
@@ -242,7 +242,7 @@ parameter_split(katom_list::const_iterator kbegin, katom_list::const_iterator ke
     return {positional, optional};
 }    
 
-void Parameter_set::parse_parameters(const katom_list& katoms, const Argtype_set& argtypes)
+void Parameter_set::parse_parameters(const katom_list& katoms, const Argtype_registry& argtypes)
 {
     (void)K::log(3, trim(katoms));
     if (katoms.empty()) {
@@ -274,10 +274,10 @@ void Parameter_set::parse_parameters(const katom_list& katoms, const Argtype_set
 }
 
 void describe_arguments(
-    std::string label,
-    std::vector<std::vector<Katom>> positional,
-    std::vector<std::vector<Katom>> optional,
-    std::vector<Katom> rest)
+    const std::string& label,
+    const std::vector<std::vector<Katom>>& positional,
+    const std::vector<std::vector<Katom>>& optional,
+    const std::vector<Katom>& rest)
 {
     std::cout << label << ":\n"
               << "  positional: " << positional << "\n"
diff --git a/mac/argument_set.h b/mac/argument_set.h
index 4b424bf..7bbf4e7 100644
--- a/mac/argument_set.h
+++ b/mac/argument_set.h
@@ -7,7 +7,7 @@
 #include "argument.h"
 #include "locator.h"
 
-class Argtype_set;
+class Argtype_registry;
 
 std::tuple<std::vector<std::vector<Katom>>,std::vector<std::vector<Katom>>,std::vector<Katom>>
 argument_split(std::vector<Katom>::const_iterator kbegin, std::vector<Katom>::const_iterator kend,
@@ -20,9 +20,9 @@ public:
     ~Parameter_set() = default;
     Parameter_set(const std::string parameter_string);
     Parameter_set(const std::vector<Katom>& katoms);
-    Parameter_set(const std::vector<Katom>& katoms, const Argtype_set& argtypes);
+    Parameter_set(const std::vector<Katom>& katoms, const Argtype_registry& argtypes);
 
-    void parse_parameters(const std::vector<Katom>& katoms, const Argtype_set& argtypes);
+    void parse_parameters(const std::vector<Katom>& katoms, const Argtype_registry& argtypes);
     void describe_parameters();
 
     void check_positional(
@@ -40,7 +40,7 @@ public:
     bool empty() const { return m_katoms.size() == 0; };
 
     std::vector<Katom> m_katoms {};
-    //Argtype_set m_argtypes {};
+    //Argtype_registry m_argtypes {};
     std::vector<Parameter> m_positional {};
     std::vector<Parameter> m_optional {};
     std::vector<std::string> m_optional_names {};
@@ -56,10 +56,10 @@ bool operator==(Parameter_set lhs, Parameter_set rhs);
 using Argument_set = Parameter_set;
 
 void describe_arguments(
-    std::string label,
-    std::vector<std::vector<Katom>> positional,
-    std::vector<std::vector<Katom>> optional,
-    std::vector<Katom> rest);
+    const std::string& label,
+    const std::vector<std::vector<Katom>>& positional,
+    const std::vector<std::vector<Katom>>& optional,
+    const std::vector<Katom>& rest);
 
 std::string replace_arguments(
     const std::map<std::string, std::string>& values,
diff --git a/mac/argv.cpp b/mac/argv.cpp
index 43cfa32..cb13ea8 100644
--- a/mac/argv.cpp
+++ b/mac/argv.cpp
@@ -227,7 +227,7 @@ void Argv::usage(const std::string& command)
 }
 
 
-void Argv::check_flags_and_options(std::string command, strings_t& words)
+void Argv::check_flags_and_options(const std::string& command, strings_t& words)
 {
     std::vector<std::string> not_defined {};
     for (auto word : words) {
@@ -334,10 +334,10 @@ void Argv::parse_optional(strings_t& words, string_map& named_args)
     // std::cout << "\n";
 }
 
-void Argv::parse_positional(std::string command, //strings_t words,
+void Argv::parse_positional(const std::string& command, //strings_t words,
                             std::string pos_args, string_map& named_args)
 {
-    for (std::string req : m_req_names) {
+    for (const std::string& req : m_req_names) {
         auto arg = m_args[req];
         auto [substring, rest, found] = regex_split_prefix(arg.m_rgx, pos_args);
         if (!found) {
diff --git a/mac/argv.h b/mac/argv.h
index bfa5103..ba135ce 100644
--- a/mac/argv.h
+++ b/mac/argv.h
@@ -62,7 +62,7 @@ public:
 
     void update_width(Arg arg);
 
-    void check_flags_and_options(std::string command, std::vector<std::string>& words);
+    void check_flags_and_options(const std::string& command, std::vector<std::string>& words);
     void parse_flags(std::vector<std::string>& words, std::map<std::string, std::string>& named_args);
     void parse_optional(std::vector<std::string>& words, std::map<std::string, std::string>& named_args);
     void parse_vars(std::vector<std::string>& words, std::map<std::string, std::string>& named_args);
@@ -72,7 +72,7 @@ public:
     bool given(const std::string& name) { return m_given.contains(name); };
 
     void parse_positional(
-        std::string command, // std::vector<std::string> words,
+        const std::string& command, // std::vector<std::string> words,
         std::string pos_args, std::map<std::string, std::string>& named_args);
 
     std::map<std::string, std::string> classify_arguments(int argc, char* argv[], bool full_parse=true);
@@ -96,11 +96,11 @@ public:
     void describe();
 //    void describe(Argv original);
 
-    bool is_flag(std::string name) {
+    bool is_flag(const std::string& name) const {
         return std::ranges::count(m_flag_names, name) > 0;
     }
 
-    bool is_opt(std::string name) {
+    bool is_opt(const std::string& name) const {
         return std::ranges::count(m_opt_names, name) > 0;
     }
 
diff --git a/mac/basenames.mk b/mac/basenames.mk
index a6347df..3132381 100644
--- a/mac/basenames.mk
+++ b/mac/basenames.mk
@@ -1 +1 @@
-BASENAMES := util error locator file argv character ktype katom katom_list log show command argument argument_set argtype argtype_set state eval eval_python eval_cpp klammer klammer_set target target_set machine
+BASENAMES := util error locator file argv character ktype katom katom_list log show command argument argument_set argtype argtype_registry state eval eval_python eval_cpp klammer klammer_registry klammerset klammerset_registry target target_registry machine
diff --git a/mac/error.h b/mac/error.h
index 8b5147b..f15cf6c 100644
--- a/mac/error.h
+++ b/mac/error.h
@@ -10,8 +10,8 @@ inline std::string command_pathname { "Pathname of command executed on the comma
 
 class Error : std::exception {
 public:
-    Error(std::string error_type, std::string description,
-          Locator locator = Locator(), bool do_justify = true)
+    Error(const std::string& error_type, const std::string& description,
+          const Locator& locator = Locator(), bool do_justify = true)
         : m_type(error_type)
         , m_desc(description)
         , m_loc(locator)
@@ -48,6 +48,13 @@ public:
         : Error("target", description, locator, do_justify) {};
 };
 
+class Klammerset_error : public Error {
+public:
+    explicit Klammerset_error(
+        const std::string& description, const Locator& locator=Locator(), bool do_justify=true)
+        : Error("klammerset", description, locator, do_justify) {};
+};
+
 class Definition_error : public Error {
 public:
     explicit Definition_error(
diff --git a/mac/eval.h b/mac/eval.h
index 454881b..87be4c6 100644
--- a/mac/eval.h
+++ b/mac/eval.h
@@ -14,7 +14,7 @@ enum class eval_t {
 class Eval
 {
 public:
-    explicit Eval(Machine& machine, Locator loc)
+    explicit Eval(Machine& machine, const Locator& loc)
         : m_machine(machine),
           m_loc(loc)
         {};
diff --git a/mac/eval_cpp.cpp b/mac/eval_cpp.cpp
index ee20c26..9181a40 100644
--- a/mac/eval_cpp.cpp
+++ b/mac/eval_cpp.cpp
@@ -7,14 +7,14 @@
 #include "file.h"
 #include "show.h"
 
-Eval_cpp::Eval_cpp(Machine& machine, Locator loc)
+Eval_cpp::Eval_cpp(Machine& machine, const Locator& loc)
     : m_machine(machine)
     , m_loc(loc)
 {
     (void)K::log(3);
 }
 
-std::string Eval_cpp::eval(fs::path library_path, std::string function_name)
+std::string Eval_cpp::eval(const fs::path& library_path, const std::string& function_name)
 {
     (void)K::log(3, library_path, function_name);
     // msg() << "library path: " << library_path.string().c_str() << "\n";
diff --git a/mac/eval_cpp.h b/mac/eval_cpp.h
index 76943e1..e2d503e 100644
--- a/mac/eval_cpp.h
+++ b/mac/eval_cpp.h
@@ -7,12 +7,12 @@
 class Eval_cpp
 {
 public:
-    explicit Eval_cpp(Machine& machine, Locator loc);
+    explicit Eval_cpp(Machine& machine, const Locator& loc);
     Eval_cpp(const Eval_cpp&) = delete;
     Eval_cpp& operator=(const Eval_cpp&) = delete;
     //~Eval_cpp();
 
-    std::string eval(fs::path library_path, std::string function_name);
+    std::string eval(const fs::path& library_path, const std::string& function_name);
 
     Machine m_machine {};
     Locator m_loc;
diff --git a/mac/eval_python.cpp b/mac/eval_python.cpp
index 0dcfea6..10564a2 100644
--- a/mac/eval_python.cpp
+++ b/mac/eval_python.cpp
@@ -5,7 +5,7 @@
 
 std::regex Eval_python::statement_delimiter("\\s*;\\s*");
 
-Eval_python::Eval_python(Machine& machine, Locator loc)
+Eval_python::Eval_python(Machine& machine, const Locator& loc)
     : m_machine(machine)
     , m_loc(loc)
     , m_globals(nullptr)
@@ -93,7 +93,7 @@ strings_t Eval_python::parse_modules(std::string code)
     return modules;
 }    
 
-void Eval_python::import_module(std::string module_name, bool verify)
+void Eval_python::import_module(const std::string& module_name, bool verify)
 {
     (void)K::log(3, module_name);
 
@@ -176,12 +176,12 @@ std::string Eval_python::get_result(PyObject* result_object)
     return result;
 }
 
-std::string Eval_python::eval_expression(std::string expression, bool import_modules)
+std::string Eval_python::eval_expression(const std::string& expression, bool import_modules)
 {
     (void)K::log(3, expression);
     // msg() << "expression: " << expression << "\n";
     if (import_modules && expression.find('.') != std::string::npos) {
-        for (auto m : parse_modules(expression)) {
+        for (const auto& m : parse_modules(expression)) {
             import_module(m);
         }
     }
@@ -191,7 +191,7 @@ std::string Eval_python::eval_expression(std::string expression, bool import_mod
             Py_eval_input, m_globals, m_locals));
 }
 
-std::string Eval_python::eval_statements(std::string script)
+std::string Eval_python::eval_statements(const std::string& script)
 {
     (void)K::log(3);
     strings_t statements = regex_split(script, statement_delimiter);
diff --git a/mac/eval_python.h b/mac/eval_python.h
index 292cd32..ad00f7d 100644
--- a/mac/eval_python.h
+++ b/mac/eval_python.h
@@ -9,16 +9,16 @@ class Eval_python
 {
 public:
     static std::regex statement_delimiter;
-    explicit Eval_python(Machine& machine, Locator loc);
+    explicit Eval_python(Machine& machine, const Locator& loc);
     Eval_python(const Eval_python&) = delete;
     Eval_python& operator=(const Eval_python&) = delete;
     ~Eval_python();
     void add_module_path(const std::string& path);
     std::vector<std::string> parse_modules(std::string code);
-    void import_module(std::string module_name, bool verify = true);
+    void import_module(const std::string& module_name, bool verify = true);
     std::string get_result(PyObject* result_object);
-    std::string eval_expression(std::string expression,  bool import_modules = true);
-    std::string eval_statements(std::string script);
+    std::string eval_expression(const std::string& expression, bool import_modules = true);
+    std::string eval_statements(const std::string& script);
     std::string eval(std::string code);
     //std::string eval_katom_list(const katom_iter& begin, const katom_iter& end);
     std::string eval_katom_list(
diff --git a/mac/file.cpp b/mac/file.cpp
index c0972ec..420d1b6 100644
--- a/mac/file.cpp
+++ b/mac/file.cpp
@@ -440,7 +440,7 @@ strings_t get_sks_directories(const std::string& s, bool include_argument)
     return result;
 }
 
-std::string cache_directory(std::string subdirectory, std::string parent_directory)
+std::string cache_directory(const std::string& subdirectory, std::string parent_directory)
 {
     if (parent_directory.empty()) {
         // /dev/shm is a fast RAM-backed tmpfs on Linux; it does not exist on
@@ -475,7 +475,7 @@ bool in_modification_order(std::string filename1, std::string filename2)
     }
 }
 
-void write_to_cache(std::string cache_dir, std::string basename, std::string text)
+void write_to_cache(const std::string& cache_dir, const std::string& basename, const std::string& text)
 {
     if (!file_exists(cache_dir)) {
         //std::cout << "Creating cache directory: " << cache_dir << "\n";
@@ -486,14 +486,14 @@ void write_to_cache(std::string cache_dir, std::string basename, std::string tex
     string_to_file(output_filename, text);
 }
 
-std::string read_from_cache(std::string cache_dir, std::string basename)
+std::string read_from_cache(const std::string& cache_dir, const std::string& basename)
 {
     std::string input_filename = cache_dir + "/" + basename;
     // msg() << "Reading file from cache: " << input_filename << "\n";
     return string_from_file(input_filename);
 }
 
-bool cache_requires_update(std::string cache_dir, std::string file_to_cache, std::string basename)
+bool cache_requires_update(const std::string& cache_dir, const std::string& file_to_cache, const std::string& basename)
 {
     std::string cache_filename = cache_dir + "/" + basename;
     return !in_modification_order(file_to_cache, cache_filename);
@@ -662,11 +662,12 @@ void copy_file_stream(const fs::path& src, const fs::path& dst)
 }
 
 void copy_preserving_basename(
-    strings_t filenames, std::string output_directory, std::string link_directory)
+    const strings_t& filenames, const std::string& output_directory,
+    const std::string& link_directory)
 {
     fs::path outdir(output_directory + "/" + link_directory);
     fs::create_directories(outdir);
-    for (std::string filename : filenames) {
+    for (const std::string& filename : filenames) {
         fs::path pname(filename);
         auto out_path = outdir / pname.filename();
         // Preserve the previous copy_options::update_existing behavior: skip
diff --git a/mac/file.h b/mac/file.h
index d69666d..888e4bb 100644
--- a/mac/file.h
+++ b/mac/file.h
@@ -45,12 +45,12 @@ fs::path klammertext_filename(
     const std::string& basename, bool error_if_missing=true, bool make_directory_if_missing=false);
 std::vector<std::string> sks_dirs();
 std::vector<std::string> get_sks_directories(const std::string& s, bool include_argument=true);
-std::string cache_directory(std::string subdirectory, std::string parent_directory="");
+std::string cache_directory(const std::string& subdirectory, std::string parent_directory="");
 std::time_t to_time_t(const fs::file_time_type& ftime);
 bool in_modification_order(std::string filename1, std::string filename2);
-void write_to_cache(std::string cache_dir, std::string basename, std::string text);
-std::string read_from_cache(std::string cache_dir, std::string basename);
-bool cache_requires_update(std::string cache_dir, std::string file_to_cache, std::string basename);
+void write_to_cache(const std::string& cache_dir, const std::string& basename, const std::string& text);
+std::string read_from_cache(const std::string& cache_dir, const std::string& basename);
+bool cache_requires_update(const std::string& cache_dir, const std::string& file_to_cache, const std::string& basename);
 
 std::vector<fs::path> pathnames_with_extension(
     const fs::path& dir, const std::string extension
@@ -73,6 +73,7 @@ bool files_differ(const fs::path& p1,
 void copy_file_stream(const fs::path& src, const fs::path& dst);
 
 void copy_preserving_basename(
-    std::vector<std::string> filenames, std::string output_directory, std::string link_directory);
+    const std::vector<std::string>& filenames, const std::string& output_directory,
+    const std::string& link_directory);
 
 fs::path resolve_relative_to(const fs::path& relative, const fs::path& base=std::filesystem::current_path());
diff --git a/mac/font_store.cpp b/mac/font_store.cpp
index 3326aef..97a9b18 100644
--- a/mac/font_store.cpp
+++ b/mac/font_store.cpp
@@ -36,7 +36,7 @@ static std::string lower_extension(const fs::path& path)
 }
 
 
-std::string name_to_dirname(std::string name)
+std::string name_to_dirname(const std::string& name)
 {
     std::string result {};
     for (char c : name) {
@@ -206,7 +206,7 @@ static void extract_font_metrics(Resolved_font& font)
     }
 }
 
-Resolved_font resolve_font(std::string family_name)
+Resolved_font resolve_font(const std::string& family_name)
 {
     if (family_name.empty())
         return {};
diff --git a/mac/font_store.h b/mac/font_store.h
index 73269a8..5e4ee49 100644
--- a/mac/font_store.h
+++ b/mac/font_store.h
@@ -19,7 +19,7 @@ struct Resolved_font {
     float capheight_ratio = 0.0f;  // cap-height / unitsPerEm from OS/2 table
 };
 
-std::string name_to_dirname(std::string name);
+std::string name_to_dirname(const std::string& name);
 // Directories searched for installed fonts (KLAMMERTEXT_FONTS, default
 // ~/.klammertext/fonts); the default font set is searched after them.
 std::vector<std::string> installed_font_dirs();
@@ -27,7 +27,7 @@ std::vector<std::string> installed_font_dirs();
 std::string default_font_dir();
 // Every installable font family found across those directories.
 std::vector<std::string> available_font_families();
-Resolved_font resolve_font(std::string family_name);
+Resolved_font resolve_font(const std::string& family_name);
 void install_resolved_font(const Resolved_font& font, std::string output_dir);
 
 // One font file classified by its internal metadata (name table, OS/2).
diff --git a/mac/katom.cpp b/mac/katom.cpp
index 5599021..9f869cd 100644
--- a/mac/katom.cpp
+++ b/mac/katom.cpp
@@ -281,7 +281,7 @@ katom_list trim(const katom_list& katoms, bool trim_inactive)
     return trim(result, trim_types);
 }
 
-strings_t line_split(std::string s)
+strings_t line_split(const std::string& s)
 {
     std::istringstream is(s);
     strings_t result {};
@@ -293,7 +293,7 @@ strings_t line_split(std::string s)
     return result;
 }
 
-std::pair<std::string, strings_t> line_split(fs::path pathname)
+std::pair<std::string, strings_t> line_split(const fs::path& pathname)
 {
     std::string source {};
     strings_t lines {};
diff --git a/mac/katom.h b/mac/katom.h
index 2e1d8f2..6de9c09 100644
--- a/mac/katom.h
+++ b/mac/katom.h
@@ -99,8 +99,8 @@ std::vector<Katom> trim(const std::vector<Katom>& katoms, bool trim_inactive = f
 
 std::vector<std::vector<Katom>> bar_split(std::vector<Katom>::iterator kbegin, std::vector<Katom>::iterator kend);
 
-std::vector<std::string> line_split(std::string s);
-std::pair<std::string, std::vector<std::string>> line_split(fs::path pathname);
+std::vector<std::string> line_split(const std::string& s);
+std::pair<std::string, std::vector<std::string>> line_split(const fs::path& pathname);
 std::vector<Katom> katomize(const std::vector<std::string>& lines, const std::string& source_desc);
 
 void warn_unparsed_katoms(std::vector<Katom>& katoms, bool warn = true);
diff --git a/mac/katom_list.cpp b/mac/katom_list.cpp
index e204555..e822149 100644
--- a/mac/katom_list.cpp
+++ b/mac/katom_list.cpp
@@ -181,10 +181,10 @@ void check_named_katom_span(const Katom& begin, const Katom& end)
 
 spans_t find_spans(
     katom_iter begin, katom_iter end,
-    std::function<bool(const Katom&)> level_inc,
-    std::function<bool(const Katom&)> level_dec,
+    const std::function<bool(const Katom&)>& level_inc,
+    const std::function<bool(const Katom&)>& level_dec,
     bool error_exit,
-    std::string name)
+    const std::string& name)
 {
     (void)K::log(4, name);
     bool _dbg = false;
@@ -245,10 +245,10 @@ spans_t find_spans(
 
 spans_t find_spans(
     katom_list& katoms,
-    std::function<bool(const Katom&)> level_inc,
-    std::function<bool(const Katom&)> level_dec,
+    const std::function<bool(const Katom&)>& level_inc,
+    const std::function<bool(const Katom&)>& level_dec,
     bool error_exit,
-    std::string name)
+    const std::string& name)
 {
     return find_spans(katoms.begin(), katoms.end(), level_inc, level_dec, error_exit, name);
 }
diff --git a/mac/katom_list.h b/mac/katom_list.h
index 06b5d47..7b4f2cd 100644
--- a/mac/katom_list.h
+++ b/mac/katom_list.h
@@ -23,17 +23,17 @@ find_katom(const std::vector<Katom>::iterator begin, const std::vector<Katom>::i
 
 std::vector<std::pair<Katom, Katom>>
 find_spans(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end,
-           std::function<bool(const Katom&)> level_inc,
-           std::function<bool(const Katom&)> level_dec,
+           const std::function<bool(const Katom&)>& level_inc,
+           const std::function<bool(const Katom&)>& level_dec,
            bool error_exit,
-           std::string name);
+           const std::string& name);
 
 std::vector<std::pair<Katom, Katom>>
 find_spans(std::vector<Katom>& katoms,
-           std::function<bool(const Katom&)> level_inc,
-           std::function<bool(const Katom&)> level_dec,
+           const std::function<bool(const Katom&)>& level_inc,
+           const std::function<bool(const Katom&)>& level_dec,
            bool error_exit=true,
-           std::string name="all");
+           const std::string& name="all");
 
 
 void describe_spans(const std::vector<Katom>& katoms);
diff --git a/mac/klammer.cpp b/mac/klammer.cpp
index 76352e5..60176f6 100644
--- a/mac/klammer.cpp
+++ b/mac/klammer.cpp
@@ -13,7 +13,7 @@ using namespace std::literals;
 std::regex Klammer::name_re = std::regex(R"((\w+)(?:\.(\w+))?)");
 
 std::tuple<std::string, std::string>
-parse_name(Target_set targets, Katom name_katom)
+parse_name(const Target_registry& targets, const Katom& name_katom)
 {
     std::string name_with_target = trim_char(name_katom.m_text, '@');
     std::smatch match {};
@@ -29,7 +29,7 @@ parse_name(Target_set targets, Katom name_katom)
     std::string klammer_name = match[1];
     std::string target_name = match[2];
     if (target_name.empty()) {
-        target_name = Target_set::general_name;
+        target_name = Target_registry::general_name;
     }
     if (!targets.has(target_name)) {
         throw Target_error(
@@ -41,7 +41,7 @@ parse_name(Target_set targets, Katom name_katom)
 }
 
 std::tuple<Katom, Parameter_set, katom_list, Locator>
-parse_definition_katoms(std::string klammer_name, Argtype_set argtypes, katom_iter& begin, katom_iter& end)
+parse_definition_katoms(const std::string& klammer_name, const Argtype_registry& argtypes, katom_iter& begin, katom_iter& end)
 {
     (void)K::log(3, *begin, *(end - 1));
     katom_iter deftype = std::find_if(
@@ -84,7 +84,7 @@ parse_definition_katoms(std::string klammer_name, Argtype_set argtypes, katom_it
 }
 
 void Klammer::add_target_definition(
-    std::string target_name, Argtype_set argtypes, katom_iter begin, katom_iter end)
+    const std::string& target_name, const Argtype_registry& argtypes, katom_iter begin, katom_iter end)
 {
     (void)K::log(3, *begin, *(end-1));
     auto [deftype, parameters, body, loc] =
@@ -95,7 +95,7 @@ void Klammer::add_target_definition(
     std::regex variable_re(R"(\*(\w+)\*)");
     int i = 0;
     variable_map_t varmap {};
-    for (auto k : body) {
+    for (const auto& k : body) {
         std::smatch match {};
         std::string txt = k.m_text;
         while (std::regex_search(txt, match, variable_re) &&
@@ -127,23 +127,23 @@ void Klammer::remove_target_definition(const std::string& target_name)
 
 // Rationalize multiple definitions
 
-std::string error_list(std::string label, auto components, std::string after="")
+std::string error_list(const std::string& label, const auto& components, const std::string& after="")
 {
     std::stringstream ss {};
     ss << label << ":\n";
-    for (auto c : components) {
+    for (const auto& c : components) {
         ss << "  " << c.loc.desc() << "\n";
     }
     ss << after;
     return ss.str();
 }
 
-auto Klammer::target_defs(std::vector<std::string> target_names)
+auto Klammer::target_defs(const std::vector<std::string>& target_names)
 {
     std::vector<Klammer::components> defs {};
-    for (auto target : target_names) {
+    for (const auto& target : target_names) {
         auto target_defs = collect_if(
-            m_defs, [target](const auto& def) { return def.target == target; });
+            m_defs, [&target](const auto& def) { return def.target == target; });
         defs.insert(defs.end(), target_defs.begin(), target_defs.end());
     }
     return defs;
@@ -173,7 +173,7 @@ void Klammer::disallow_instances() //Klammer::components declaration)
     }
 }
 
-bool Klammer::copy_to_instances(Target_set targets)
+bool Klammer::copy_to_instances(const Target_registry& targets)
 {
     auto instances = instance_defs();
     if (!instances.empty()) {
@@ -202,19 +202,20 @@ bool Klammer::copy_to_instances(Target_set targets)
 }
 
 void Klammer::copy_components(
-    Parameter_set parameters, std::vector<Klammer::components> cs, Target_set targets)
+    const Parameter_set& parameters, const std::vector<Klammer::components>& cs,
+    const Target_registry& targets)
 {
     (void)K::log(4);
-    for (auto target_name : targets.m_names) {
-        if (target_name == Target_set::declare_name ||
-            target_name == Target_set::general_name) {
+    for (const auto& target_name : targets.m_names) {
+        if (target_name == Target_registry::declare_name ||
+            target_name == Target_registry::general_name) {
             continue;
         }
         m_parameters = parameters;
     }
-    for (auto c : cs) {
+    for (const auto& c : cs) {
         m_body[c.target] = c.body;
-        m_body_generic[c.target] = (c.target == Target_set::general_name);
+        m_body_generic[c.target] = (c.target == Target_registry::general_name);
         m_varmap[c.target] = c.varmap;
     }
 }
@@ -223,7 +224,7 @@ void Klammer::copy_components(
 
 void Klammer::check_for_multiple_general_klammers()
 {
-    auto general_klammers = target_defs({Target_set::general_name});
+    auto general_klammers = target_defs({Target_registry::general_name});
     if (general_klammers.size() > 1) {
         throw Definition_error(
             error_list(
@@ -235,11 +236,11 @@ void Klammer::check_for_multiple_general_klammers()
 
 void Klammer::check_for_declaration_and_definitions()
 {
-    auto declares = target_defs({Target_set::declare_name});
+    auto declares = target_defs({Target_registry::declare_name});
     if (!declares.empty()) {
         std::vector<Klammer::components> definitions {};
-        for (auto def : m_defs) {
-            if (def.target != Target_set::declare_name) {
+        for (const auto& def : m_defs) {
+            if (def.target != Target_registry::declare_name) {
                 if (def.deftype == katom_t::klammer_definition ||
                     def.deftype == katom_t::klammer_default) {
                     msg() << def << "\n";
@@ -261,11 +262,11 @@ void Klammer::check_for_declaration_and_definitions()
 
 // If a general definition exists, use it for targets not defined, but check signatures
 
-void Klammer::copy_general_klammer_to_undefined(Target_set targets)
+void Klammer::copy_general_klammer_to_undefined(const Target_registry& targets)
 {
     (void)K::log(4);
-    auto general_klammers = target_defs({Target_set::general_name});
-    auto declares = target_defs({Target_set::declare_name});
+    auto general_klammers = target_defs({Target_registry::general_name});
+    auto declares = target_defs({Target_registry::declare_name});
 
     // Check matching signatures (though this case already handled)
     if (general_klammers.size() == 1) {
@@ -279,13 +280,13 @@ void Klammer::copy_general_klammer_to_undefined(Target_set targets)
                     m_parameters.m_katoms[0].m_loc, false);
             }
         }
-        auto [target, deftype, parameters, body, varmap, loc] = general_klammers[0];
+        const auto& [target, deftype, parameters, body, varmap, loc] = general_klammers[0];
         if (m_parameters.m_katoms.empty()) {
             m_parameters = parameters;
         }
-        for (auto target_name : targets.m_names) {
+        for (const auto& target_name : targets.m_names) {
             // std::cout << "General copy, considering " << target_name << "\n";
-            if (m_body.count(target_name) == 0 && target_name != Target_set::declare_name) {
+            if (m_body.count(target_name) == 0 && target_name != Target_registry::declare_name) {
                 // std::cout << "  Copying to " << target_name << "\n";
                 m_body[target_name] = body;
                 m_body_generic[target_name] = true; // general body -> writer content
@@ -298,7 +299,7 @@ void Klammer::copy_general_klammer_to_undefined(Target_set targets)
 
 // Three declaration cases: none, one, many
 
-void Klammer::no_declarations(Target_set targets)
+void Klammer::no_declarations(const Target_registry& targets)
 {
     (void)K::log(4);
     // std::cout << boldblack << "No declarations\n" << black;
@@ -308,7 +309,7 @@ void Klammer::no_declarations(Target_set targets)
     std::vector<std::string> target_names = targets.applicable();
     std::vector<Parameter_set> all_parameter_sets {};
     // Are all parameters the same?
-    for (auto def : m_defs) {
+    for (const auto& def : m_defs) {
         if (std::ranges::find(target_names, def.target) != target_names.end()) {
             // std::cout << "  Found: " << def.target << "\n";
             all_parameter_sets.push_back(def.parameters);
@@ -332,7 +333,7 @@ void Klammer::no_declarations(Target_set targets)
     copy_general_klammer_to_undefined(targets);
 }
 
-void Klammer::one_declaration(Target_set targets, Klammer::components declare)
+void Klammer::one_declaration(const Target_registry& targets, const Klammer::components& declare)
 {
     (void)K::log(4);
     // std::cout << boldblack << "One declaration\n" << black;
@@ -342,7 +343,7 @@ void Klammer::one_declaration(Target_set targets, Klammer::components declare)
     copy_general_klammer_to_undefined(targets);
 }
 
-void Klammer::many_declarations(std::vector<Klammer::components> declares)
+void Klammer::many_declarations(const std::vector<Klammer::components>& declares)
 {
     (void)K::log(4);
     // std::cout << boldblack << "Many declarations\n" << black;
@@ -353,10 +354,10 @@ void Klammer::many_declarations(std::vector<Klammer::components> declares)
 
 
 
-void Klammer::rationalize(Target_set targets)
+void Klammer::rationalize(const Target_registry& targets)
 {
     (void)K::log(3, m_name);
-    auto declares = target_defs({Target_set::declare_name});
+    auto declares = target_defs({Target_registry::declare_name});
     auto declare_count = declares.size();
     if (declare_count == 0) {
         disallow_instances();
@@ -371,7 +372,7 @@ void Klammer::rationalize(Target_set targets)
 }    
 
 
-std::string klammer_name_from_katom(std::string s, Locator loc)
+std::string klammer_name_from_katom(const std::string& s, const Locator& loc)
 {
     std::regex rgx(R"(@(\w+).*)");
     std::smatch match {};
@@ -389,11 +390,11 @@ void label(const std::string& s)
     std::cout << std::right << std::setw(w) << std::setfill(' ') << s << ": ";
 }
 
-void show_args(const std::string& label_text, std::vector<Argument> arguments)
+void show_args(const std::string& label_text, const std::vector<Argument>& arguments)
 {
     if (!arguments.empty()) {
         label(label_text);
-        for (auto a : arguments) {
+        for (const auto& a : arguments) {
             std::cout << a << " ";
         }
         std::cout << '\n';
@@ -403,7 +404,7 @@ void show_args(const std::string& label_text, std::vector<Argument> arguments)
 strings_t Klammer::get_target_names() const
 {
     strings_t names {};
-    for (auto [target, body] : m_body) {
+    for (const auto& [target, body] : m_body) {
         std::stringstream ss {};
         // ss << name << target.m_loc.m_line;
         ss << target;
@@ -422,12 +423,12 @@ strings_t Klammer::get_locations()
     return {};
 }
 
-std::string Klammer::signature_text()
+std::string Klammer::signature_text() const
 {
     std::string result {};
     bool has_pos = false;
     bool has_opt = false;
-    for (auto pos : m_parameters.m_positional) {
+    for (const auto& pos : m_parameters.m_positional) {
         result += pos.m_name;
         std::string type = pos.m_argtype.m_name;
         if (type != default_argtype) {
@@ -442,7 +443,7 @@ std::string Klammer::signature_text()
     if (opt_count <= 3 && !has_pos) {
         result += " ";
     }
-    for (auto opt : m_parameters.m_optional) {
+    for (const auto& opt : m_parameters.m_optional) {
         if (opt_count > 3) {
             result += "\n   :" + opt.m_name;
         } else {
@@ -473,18 +474,18 @@ std::string Klammer::signature_text()
 }
 
 
-std::string Klammer::description_text()
+std::string Klammer::description_text() const
 {
     std::string result = " [" + m_name + ": no description]";
     if (m_body.contains("k")) {
-        result = to_string(m_body["k"], true);
+        result = to_string(m_body.at("k"), true);
         result = justify(result, 80, 1);
     }
     return result;
 }
 
 
-std::string Klammer::describe(int margin)
+std::string Klammer::describe(int margin) const
 {
     std::string result {};
     result += "@" + m_name + signature_text() + description_text();
diff --git a/mac/klammer.h b/mac/klammer.h
index e6e4628..1e17987 100644
--- a/mac/klammer.h
+++ b/mac/klammer.h
@@ -4,7 +4,7 @@
 
 #include "deftype.h"
 #include "argument_set.h"
-#include "target_set.h"
+#include "target_registry.h"
 #include "locator.h"
 
 class Klammer
@@ -31,37 +31,38 @@ public:
     // target-name -> [variable -> index]
 
     void add_target_definition(
-        std::string target_name, Argtype_set argtypes,
+        const std::string& target_name, const Argtype_registry& argtypes,
         std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end);
     void remove_target_definition(const std::string& target_name);
 
-    auto target_defs(std::vector<std::string> target_names);
+    auto target_defs(const std::vector<std::string>& target_names);
     auto instance_defs();
     void disallow_instances(); //Klammer::components declaration);
-    bool copy_to_instances(Target_set targets);
+    bool copy_to_instances(const Target_registry& targets);
     void copy_components(
-        Parameter_set parameters, std::vector<Klammer::components> cs, Target_set targets);
+        const Parameter_set& parameters, const std::vector<Klammer::components>& cs,
+        const Target_registry& targets);
     void check_for_multiple_general_klammers();
     void check_for_declaration_and_definitions();
-    void copy_general_klammer_to_undefined(Target_set targets);
-    void no_declarations(Target_set targets);
-    void one_declaration(Target_set targets, Klammer::components declare);
-    void many_declarations(std::vector<Klammer::components> declares);
-    void rationalize(Target_set target);
+    void copy_general_klammer_to_undefined(const Target_registry& targets);
+    void no_declarations(const Target_registry& targets);
+    void one_declaration(const Target_registry& targets, const Klammer::components& declare);
+    void many_declarations(const std::vector<Klammer::components>& declares);
+    void rationalize(const Target_registry& targets);
     /*
     void add_description(const std::string& desc, Katom definition_type);
 
     auto user_defs();
     auto klammer_defines_parameters();
     auto klammer_uses_parameters();
-    void check_for_target_errors(Target_set targets);
+    void check_for_target_errors(Target_registry targets);
     bool explicit_parameters_match();
-    void copy_components(Klammer::components cs, Target_set targets);
+    void copy_components(Klammer::components cs, Target_registry targets);
     */
 
-    std::string signature_text();
-    std::string description_text();
-    std::string describe(int margin=0);
+    std::string signature_text() const;
+    std::string description_text() const;
+    std::string describe(int margin=0) const;
 
     bool has_literal_param() const {
         for (const auto& p : m_parameters.m_positional)
@@ -91,18 +92,18 @@ public:
     std::map<std::string, bool> m_body_generic {};
 };
 
-std::string klammer_name_from_katom(std::string s, Locator loc);
+std::string klammer_name_from_katom(const std::string& s, const Locator& loc);
 
 std::tuple<std::string,std::string>
-parse_name(Target_set targets, Katom name_katom);
+parse_name(const Target_registry& targets, const Katom& name_katom);
 
 std::tuple<Katom, Parameter_set, std::vector<Katom>, Locator>
-parse_definition_katoms(Argtype_set argtypes,  //Target_set targets,
+parse_definition_katoms(const std::string& klammer_name, const Argtype_registry& argtypes,
                         std::vector<Katom>::iterator& begin, std::vector<Katom>::iterator& end);
 
 /*
 klammer_definition_args parse_klammer_definition_katoms(
-    katom_list& katoms, Argtype_set& argtypes);
+    katom_list& katoms, Argtype_registry& argtypes);
 
 void check_for_undefined_arguments(
     std::string name, Parameters parameters, katom_list body_katoms, Locator loc);
diff --git a/mac/klammer_set.cpp b/mac/klammer_registry.cpp
similarity index 80%
rename from mac/klammer_set.cpp
rename to mac/klammer_registry.cpp
index 0e7c51f..bf50cfd 100644
--- a/mac/klammer_set.cpp
+++ b/mac/klammer_registry.cpp
@@ -1,18 +1,18 @@
 #include "klammer.h"
-#include "klammer_set.h"
+#include "klammer_registry.h"
 #include "show.h"
 #include "util.h"
 #include "log.h"
 #include "error.h"
 
 /*
-bool Klammer_set::has(std::string name, std::string target)
+bool Klammer_registry::has(std::string name, std::string target)
 {
     return m_klammers.count(name) > 0;
 }
 */
 
-void Klammer_set::add(Argtype_set argtypes, Target_set& targets, katom_iter begin, katom_iter end, katom_list& katoms)
+void Klammer_registry::add(const Argtype_registry& argtypes, const Target_registry& targets, katom_iter begin, katom_iter end, katom_list& katoms)
 {
     (void)K::log(3, *begin, *(end - 1));
     restore_initial_type(begin, end);
@@ -62,7 +62,7 @@ void Klammer_set::add(Argtype_set argtypes, Target_set& targets, katom_iter begi
     // This add's target:
     Target target = targets.get(target_name, begin->m_loc);
     if (!target.m_provides.empty()) {
-        for (auto provide_name : target.m_provides) {
+        for (const auto& provide_name : target.m_provides) {
             if (m_klammers[klammer_name].m_defloc.count(provide_name) > 0) {
                 m_klammers[klammer_name].remove_target_definition(provide_name);
             }
@@ -80,30 +80,30 @@ void Klammer_set::add(Argtype_set argtypes, Target_set& targets, katom_iter begi
     ignore_whitespace(next_iter, katoms);
 }    
 
-void Klammer_set::rationalize(Target_set targets)
+void Klammer_registry::rationalize(const Target_registry& targets)
 {
     (void)K::log(3);
-    for (auto k : m_klammers) {
-        m_klammers[k.first].rationalize(targets);
+    for (auto& [name, klammer] : m_klammers) {
+        klammer.rationalize(targets);
     }
 }
 
 /*
-bool Klammer_set::has(std::string name, std::string target)
+bool Klammer_registry::has(std::string name, std::string target)
 {
     return m_klammers.count(name) > 0;
 }
 */
 
-void Klammer_set::check_klammer(std::string name, std::string target, Locator loc)
+void Klammer_registry::check_klammer(const std::string& name, const std::string& target, const Locator& loc) const
 {
     if (m_klammers.count(name) == 0) {
         throw Definition_error("The klammer " + q_(name) + " is not defined for an unspecified target", loc);
     }
-    Klammer k = m_klammers[name];
+    const Klammer& k = m_klammers.at(name);
     if (k.m_defloc.count(target) == 0) {
         std::string desc;
-        if (target == Target_set::general_name) {
+        if (target == Target_registry::general_name) {
             desc = "an unspecified target";
         } else {
             desc = "target " + q_(target);
@@ -113,7 +113,7 @@ void Klammer_set::check_klammer(std::string name, std::string target, Locator lo
 }
 
 
-const std::vector<Katom>* Klammer_set::constant_body(const std::string& name) const
+const std::vector<Katom>* Klammer_registry::constant_body(const std::string& name) const
 {
     auto it = m_klammers.find(name);
     if (it == m_klammers.end()) return nullptr;
@@ -126,14 +126,14 @@ const std::vector<Katom>* Klammer_set::constant_body(const std::string& name) co
         if (!d.parameters.empty()) return nullptr;
     }
     for (const auto& d : k.m_defs) {
-        if (d.target == Target_set::general_name && d.parameters.empty()) {
+        if (d.target == Target_registry::general_name && d.parameters.empty()) {
             return &d.body;
         }
     }
     return nullptr;
 }
 
-int max_length(std::map<std::string, Klammer> ss)
+int max_length(const std::map<std::string, Klammer>& ss)
 {
     size_t result = 0;
     for_each(ss.begin(), ss.end(),
@@ -141,19 +141,19 @@ int max_length(std::map<std::string, Klammer> ss)
     return result;
 }
 
-std::string Klammer_set::instance_list(int margin) const
+std::string Klammer_registry::instance_list(int margin) const
 {
     std::stringstream ss {};
     std::string tab(margin, ' ');
     auto name_width = max_length(m_klammers);
-    for (auto [name, k] : m_klammers) {
+    for (const auto& [name, k] : m_klammers) {
         ss << tab << std::setfill(' ') << std::setw(name_width) << name
            << sp_arrow << k << "\n";
     }
     return ss.str();
 }
 
-std::string Klammer_set::describe(int margin) const
+std::string Klammer_registry::describe(int margin) const
 {
     /*
     strings_t names {};
@@ -161,7 +161,7 @@ std::string Klammer_set::describe(int margin) const
     strings_t locations {};
     */
     std::string result;
-    for (auto [name, k] : m_klammers) {
+    for (const auto& [name, k] : m_klammers) {
         result += k.describe(margin) + "\n";
         /*
         names.push_back(name);
diff --git a/mac/klammer_set.h b/mac/klammer_registry.h
similarity index 54%
rename from mac/klammer_set.h
rename to mac/klammer_registry.h
index 5b6f829..75c6f2e 100644
--- a/mac/klammer_set.h
+++ b/mac/klammer_registry.h
@@ -1,16 +1,16 @@
 #pragma once
 
 #include "klammer.h"
-#include "target_set.h"
+#include "target_registry.h"
 
-class Klammer_set
+class Klammer_registry
 {
 public:
-    Klammer_set() = default;
-    void add(Argtype_set argtypes, Target_set& targets,
+    Klammer_registry() = default;
+    void add(const Argtype_registry& argtypes, const Target_registry& targets,
              std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms);
-    void rationalize(Target_set targets);
-    void check_klammer(std::string name, std::string target, Locator loc);
+    void rationalize(const Target_registry& targets);
+    void check_klammer(const std::string& name, const std::string& target, const Locator& loc) const;
     const std::vector<Katom>* constant_body(const std::string& name) const;
     std::string instance_list(int margin) const;
     std::string describe(int margin=0) const;
diff --git a/mac/klammerset.cpp b/mac/klammerset.cpp
new file mode 100644
index 0000000..933ad80
--- /dev/null
+++ b/mac/klammerset.cpp
@@ -0,0 +1,8 @@
+#include "klammerset.h"
+
+Klammerset::Klammerset(const std::string& symbol, const std::string& desc, const Locator& loc)
+    : m_symbol(symbol)
+    , m_desc(desc)
+    , m_loc(loc)
+{
+}
diff --git a/mac/klammerset.h b/mac/klammerset.h
new file mode 100644
index 0000000..c971d16
--- /dev/null
+++ b/mac/klammerset.h
@@ -0,0 +1,28 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+#include "locator.h"
+
+// A Klammerset is the formal construct declared by the @@@klammerset system
+// command: a named, logically related group of klammer definitions loaded
+// together.  The instance holds metadata and the file list only -- the
+// klammers themselves live in the Machine's Klammer_registry (one flat,
+// additive namespace; the definition modes govern collisions).  Membership
+// is provenance, not containment.
+class Klammerset
+{
+public:
+    Klammerset() = default;
+    Klammerset(const std::string& symbol, const std::string& desc, const Locator& loc);
+
+    std::string m_symbol {};   // registry key and command-line name (e.g. "sks")
+    std::string m_desc {};     // the logical relationship that makes this a set
+    std::string m_name {};     // display name (e.g. "Standard Klammer Set")
+    std::string m_author {};
+    std::string m_date {};     // last update; a date serves as the version
+    std::vector<std::string> m_requires {};  // klammerset declaration files, loaded first
+    std::vector<std::string> m_files {};     // definition files, loaded in list order
+    Locator m_loc {};          // the declaring file; relative names resolve against it
+};
diff --git a/mac/klammerset_registry.cpp b/mac/klammerset_registry.cpp
new file mode 100644
index 0000000..da5e007
--- /dev/null
+++ b/mac/klammerset_registry.cpp
@@ -0,0 +1,225 @@
+#include <cctype>
+#include <cstdlib>
+#include <iomanip>
+#include <sstream>
+
+#include "klammerset_registry.h"
+#include "error.h"
+#include "file.h"
+#include "log.h"
+#include "util.h"
+#include "show.h"
+#include "katom.h"
+
+Klammerset_registry::Klammerset_registry()
+        : m_parameters(Parameter_set("symbol | desc :name :author :date :requires :files"))
+{
+}
+
+void Klammerset_registry::add(Klammerset klammerset)
+{
+    (void)K::log(3, klammerset.m_symbol);
+    m_klammersets[klammerset.m_symbol] = klammerset;
+    m_symbols.push_back(klammerset.m_symbol);
+}
+
+std::optional<Klammerset> Klammerset_registry::add(
+    std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms)
+{
+    (void)K::log(3, *begin, *(end - 1));
+    auto [positional, optional, rest] =
+        argument_split(begin + 1, end - 1, m_parameters.m_positional.size());
+    auto values = m_parameters.value_map(positional, optional, rest, begin->m_loc);
+
+    modify_type(katom_t::replaced, begin, end);
+    auto next_iter = end;
+    ignore_whitespace(next_iter, katoms);
+
+    std::string symbol = values["symbol"];
+    check_symbol(symbol, begin->m_loc);
+    if (has(symbol)) {
+        (void)K::log(2, "Klammerset \"" + symbol + "\" is already loaded; declaration skipped");
+        return std::nullopt;
+    }
+
+    // The filename lists follow the standard conventions (spaces allowed,
+    // standalone "/" separator).  The existence rescue tests names against
+    // the declaring file's directory, where relative names are later
+    // resolved by Machine::load_klammerset_files.
+    fs::path declaring(begin->m_loc.m_filename);
+    std::string base_dir =
+        fs::exists(declaring) ? declaring.parent_path().string() : "";
+
+    Klammerset klammerset(symbol, values["desc"], begin->m_loc);
+    klammerset.m_name = values["name"];
+    klammerset.m_author = values["author"];
+    klammerset.m_date = values["date"];
+    klammerset.m_requires = resolve_filename_list(values["requires"], base_dir);
+    klammerset.m_files = resolve_filename_list(values["files"], base_dir);
+    add(klammerset);
+    return klammerset;
+}
+
+void Klammerset_registry::check_symbol(const std::string& symbol, const Locator& loc) const
+{
+    bool valid = !symbol.empty() && std::isalpha(static_cast<unsigned char>(symbol[0]));
+    for (char c : symbol) {
+        if (!std::isalnum(static_cast<unsigned char>(c)) && c != '_') {
+            valid = false;
+        }
+    }
+    if (!valid) {
+        throw Klammerset_error(
+            "The klammerset symbol \"" + symbol + "\" is not valid. A symbol begins "
+            "with a letter and contains only letters, digits, and underscores.",
+            loc);
+    }
+}
+
+bool Klammerset_registry::has(const std::string& symbol) const
+{
+    return m_klammersets.count(symbol) > 0;
+}
+
+Klammerset Klammerset_registry::get(const std::string& symbol, const Locator& loc) const
+{
+    if (has(symbol)) {
+        return m_klammersets.at(symbol);
+    } else {
+        throw Klammerset_error("Klammerset " + symbol + " does not exist", loc);
+    }
+}
+
+// --- The klammerset search path ---
+
+bool is_klammerset_symbol(const std::string& name)
+{
+    if (name.empty() || !std::isalpha(static_cast<unsigned char>(name[0]))) {
+        return false;
+    }
+    for (char c : name) {
+        if (!std::isalnum(static_cast<unsigned char>(c)) && c != '_') {
+            return false;
+        }
+    }
+    return true;
+}
+
+std::vector<std::string> klammerset_search_dirs(const std::string& local_dir)
+{
+    std::vector<std::string> result {};
+    // A repeated directory (e.g. the local stage already IS
+    // $KLAMMERTEXT_HOME) adds nothing and clutters error messages.
+    auto push_unique = [&result](const std::string& dir) {
+        std::string canonical = fs::weakly_canonical(dir).string();
+        if (!is_in(canonical, result)) {
+            result.push_back(canonical);
+        }
+    };
+    if (!local_dir.empty()) {
+        push_unique(local_dir);
+    }
+    std::string paths {};
+    const char* env = std::getenv("KLAMMERTEXT_KLAMMERSETS");
+    if (env && *env) {
+        paths = env;
+    } else if (const char* home = std::getenv("HOME"); home && *home) {
+        paths = std::string(home) + "/.klammertext/klammersets";
+    }
+    std::stringstream ss(paths);
+    std::string dir;
+    while (std::getline(ss, dir, ':')) {
+        if (!dir.empty()) {
+            push_unique(dir);
+        }
+    }
+    if (const char* kthome = std::getenv(klammertext_home_var.c_str()); kthome && *kthome) {
+        push_unique(kthome);
+    }
+    return result;
+}
+
+fs::path resolve_klammerset_symbol(
+    const std::string& symbol, const std::string& local_dir, const Locator& loc)
+{
+    std::vector<std::string> dirs = klammerset_search_dirs(local_dir);
+    for (const std::string& dir : dirs) {
+        fs::path candidate = fs::path(dir) / symbol / (symbol + ".k");
+        if (fs::exists(candidate) && fs::is_regular_file(candidate)) {
+            return fs::weakly_canonical(candidate);
+        }
+    }
+    throw Klammerset_error(
+        "The klammerset \"" + symbol + "\" was not found. A symbol x names the "
+        "declaration file x/x.k in one of the search directories: "
+        + join(dirs, ", ")
+        + ". Enter \"kdesc --klammerset\" to list the available klammersets.",
+        loc);
+}
+
+std::string describe_klammerset_search(const std::string& local_dir, int margin)
+{
+    std::string tab(margin, ' ');
+    std::stringstream ss {};
+    std::map<std::string, std::string> first_hit {};
+    for (const std::string& dir : klammerset_search_dirs(local_dir)) {
+        if (!fs::is_directory(dir)) {
+            continue;
+        }
+        for (const auto& entry : fs::directory_iterator(dir)) {
+            if (!entry.is_directory()) {
+                continue;
+            }
+            std::string symbol = entry.path().filename().string();
+            fs::path declaration = entry.path() / (symbol + ".k");
+            if (!is_klammerset_symbol(symbol) || !fs::is_regular_file(declaration)) {
+                continue;
+            }
+            ss << tab << symbol << sp_arrow << declaration.string();
+            if (first_hit.count(symbol)) {
+                ss << "  (shadowed by " << first_hit[symbol] << ")";
+            } else {
+                first_hit[symbol] = declaration.string();
+            }
+            ss << "\n";
+        }
+    }
+    if (first_hit.empty()) {
+        ss << tab << "(no klammersets found)\n";
+    }
+    return ss.str();
+}
+
+std::string Klammerset_registry::describe(int margin, bool long_format) const
+{
+    std::string tab(margin, ' ');
+    std::stringstream ss {};
+    std::vector<std::string> descs {};
+    for (const std::string& symbol : m_symbols) {
+        descs.push_back(m_klammersets.at(symbol).m_desc);
+    }
+    auto symbol_width = max_length(m_symbols);
+    auto desc_width = max_length(descs);
+    for (const std::string& symbol : m_symbols) {
+        const Klammerset& ks = m_klammersets.at(symbol);
+        if (long_format) {
+            ss << tab << std::setfill(' ') << std::setw(symbol_width) << std::left << symbol << "  "
+               << std::setw(desc_width) << std::left << ks.m_desc << "  "
+               << ks.m_loc.str() << "\n";
+            if (!ks.m_name.empty())
+                ss << tab << std::string(symbol_width, ' ') << "  name: " << ks.m_name << "\n";
+            if (!ks.m_author.empty())
+                ss << tab << std::string(symbol_width, ' ') << "  author: " << ks.m_author << "\n";
+            if (!ks.m_date.empty())
+                ss << tab << std::string(symbol_width, ' ') << "  date: " << ks.m_date << "\n";
+            if (!ks.m_requires.empty())
+                ss << tab << std::string(symbol_width, ' ') << "  requires: " << join(ks.m_requires, " / ") << "\n";
+            if (!ks.m_files.empty())
+                ss << tab << std::string(symbol_width, ' ') << "  files: " << join(ks.m_files, " / ") << "\n";
+        } else {
+            ss << tab << std::setfill(' ') << std::setw(symbol_width) << std::left << symbol
+               << sp_arrow << ks << "\n";
+        }
+    }
+    return ss.str();
+}
diff --git a/mac/klammerset_registry.h b/mac/klammerset_registry.h
new file mode 100644
index 0000000..e59dfe6
--- /dev/null
+++ b/mac/klammerset_registry.h
@@ -0,0 +1,63 @@
+#pragma once
+#include <map>
+#include <optional>
+#include <string>
+
+#include "klammerset.h"
+#include "argument_set.h"
+#include "katom.h"
+
+class Klammerset_registry
+{
+public:
+    Klammerset_registry();
+
+    void add(Klammerset klammerset);
+    // Parse a @@@klammerset span.  Returns the new Klammerset so the
+    // Machine can load its files, or nullopt when the symbol is already
+    // registered: a klammerset is loaded once, and a repeated declaration
+    // (typically reached through :requires) is skipped, not an error.
+    std::optional<Klammerset> add(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms);
+    void check_symbol(const std::string& symbol, const Locator& loc) const;
+
+    bool has(const std::string& symbol) const;
+    Klammerset get(const std::string& symbol, const Locator& loc) const;
+
+    std::string describe(int margin=2, bool long_format=false) const;
+
+    std::map<std::string, Klammerset> m_klammersets {};
+    std::vector<std::string> m_symbols {};
+    Parameter_set m_parameters {};
+};
+
+// --- The klammerset search path (symbol -> declaration file) ---
+
+// A bare identifier (letters, digits, underscores; starts with a letter)
+// names a klammerset symbol; anything else -- a path component, an
+// extension, a space -- is a filename used as given.
+bool is_klammerset_symbol(const std::string& name);
+
+// The directories searched for a klammerset symbol, most specific first:
+//   1. local_dir -- the directory of whatever names the symbol: the input
+//      document's directory (ktext -k), the declaring file's directory
+//      (:requires), or the cwd when there is no document
+//   2. the KLAMMERTEXT_KLAMMERSETS directories (colon-separated; default
+//      ~/.klammertext/klammersets), in listed order
+//   3. $KLAMMERTEXT_HOME (the distribution's sets, e.g. sks/sks.k)
+// A symbol x resolves to the first <dir>/x/x.k found, so a document-local
+// set shadows an installed one, which shadows a distributed one.  (This is
+// deliberately the OPPOSITE order from the @eval module path, which puts
+// the SKS directories first: a stray util.py next to a document shadowing
+// an SKS module is an everyday accident, while a directory named sks/
+// holding an sks.k next to a manuscript is not.)
+std::vector<std::string> klammerset_search_dirs(const std::string& local_dir);
+
+// Resolve a symbol to its declaration file; first hit wins.  Throws a
+// Klammerset_error naming the searched directories when nothing matches.
+fs::path resolve_klammerset_symbol(
+    const std::string& symbol, const std::string& local_dir, const Locator& loc);
+
+// The symbols available on the search path, with provenance; a symbol
+// found again in a later directory is marked as shadowed.  For
+// kdesc --klammerset.
+std::string describe_klammerset_search(const std::string& local_dir, int margin=2);
diff --git a/mac/locator.cpp b/mac/locator.cpp
index 1aeaed8..01a98c4 100644
--- a/mac/locator.cpp
+++ b/mac/locator.cpp
@@ -28,7 +28,7 @@ std::string abbreviate_location(
 }
 
 
-Locator::Locator(fs::path filename, int line, int chr)
+Locator::Locator(const fs::path& filename, int line, int chr)
     : m_filename(filename)
     , m_line(line)
     , m_chr(chr)
diff --git a/mac/locator.h b/mac/locator.h
index 78b8659..95b6589 100644
--- a/mac/locator.h
+++ b/mac/locator.h
@@ -23,7 +23,7 @@ public:
         , m_line(int(location.line()))
         , m_chr(int(location.column()))
         {};
-    Locator(fs::path filename, int line, int chr);
+    Locator(const fs::path& filename, int line, int chr);
     std::string str(bool relative = false) const;
     std::string desc(bool relative = false) const;
     std::string abbrev(bool include_chr=true) const;
diff --git a/mac/machine.cpp b/mac/machine.cpp
index 9434dc1..7beb73c 100644
--- a/mac/machine.cpp
+++ b/mac/machine.cpp
@@ -9,10 +9,10 @@
 #include "eval.h"
 
 Machine::Machine()
-    : m_argtypes(Argtype_set())
+    : m_argtypes(Argtype_registry())
     , m_state(State())
-    , m_targets(Target_set())
-    , m_klammers(Klammer_set())
+    , m_targets(Target_registry())
+    , m_klammers(Klammer_registry())
 {
     (void)K::log(3);
     m_state.add_environment_frame();
@@ -352,20 +352,80 @@ void Machine::extract_machine_definitions()
     if (m_katoms.empty()) {
         return;
     }
-    for (const auto& [op, cl] : find_spans(m_katoms, begin_machine_def, end_machine_def, true, command_name)) {
-        auto [begin, end] = find_span_katoms(m_katoms, op, cl);
-        //std::string name = trim_char(begin->m_text, '@');
-        std::string name = begin->m_text;
-        if (name == "@@@target") {
-            m_targets.add(begin, end, m_katoms);
-        } else if (name == "@@@argtype") {
-            m_argtypes.add(begin, end, m_katoms);
-        } else if (name == "@@@state") {
-            m_state.parse_state_katoms(begin, end, m_katoms);
+    // A @@@klammerset declaration inserts its files' katoms into the stream
+    // at the declaration point, invalidating the span list, so the scan
+    // restarts.  Processed spans are marked replaced and are never found
+    // again, which also bounds the restarts.
+    bool rescan = true;
+    while (rescan) {
+        rescan = false;
+        for (const auto& [op, cl] : find_spans(m_katoms, begin_machine_def, end_machine_def, true, command_name)) {
+            auto [begin, end] = find_span_katoms(m_katoms, op, cl);
+            //std::string name = trim_char(begin->m_text, '@');
+            std::string name = begin->m_text;
+            if (name == "@@@target") {
+                m_targets.add(begin, end, m_katoms);
+            } else if (name == "@@@argtype") {
+                m_argtypes.add(begin, end, m_katoms);
+            } else if (name == "@@@state") {
+                m_state.parse_state_katoms(begin, end, m_katoms);
+            } else if (name == "@@@klammerset") {
+                if (auto klammerset = m_klammersets.add(begin, end, m_katoms)) {
+                    load_klammerset_files(*klammerset, end);
+                    rescan = true;
+                    break;
+                }
+            }
         }
     }
 }
 
+void Machine::load_klammerset_files(const Klammerset& klammerset, katom_iter insert_at)
+{
+    (void)K::log(2, "Loading klammerset \"" + klammerset.m_symbol + "\"");
+    // Relative names resolve against the declaring file's directory, never
+    // the cwd.  :requires files are read before the set's own files; each
+    // holds its own @@@klammerset declaration, whose already-loaded guard
+    // makes repeated requirements a no-op.
+    fs::path declaring(klammerset.m_loc.m_filename);
+    fs::path base = fs::exists(declaring) ? declaring : fs::current_path();
+    std::string base_dir = (is_directory(base) ? base : base.parent_path()).string();
+
+    // A :requires entry may be a bare symbol, resolved on the klammerset
+    // search path with the declaring directory as the local stage; :files
+    // entries are always filenames (this set's own definition files).
+    std::vector<std::string> filenames {};
+    for (const auto& required : klammerset.m_requires) {
+        if (is_klammerset_symbol(required)) {
+            filenames.push_back(
+                resolve_klammerset_symbol(required, base_dir, klammerset.m_loc).string());
+        } else {
+            filenames.push_back(required);
+        }
+    }
+    filenames.insert(filenames.end(), klammerset.m_files.begin(), klammerset.m_files.end());
+
+    // Collect all files into one list and insert once: insert_at is
+    // invalidated by the first insertion into m_katoms.
+    katom_list loaded {};
+    for (const auto& filename : filenames) {
+        fs::path pathname = resolve_relative_to(filename, base);
+        if (!fs::exists(pathname)) {
+            throw Klammerset_error(
+                "Klammerset \"" + klammerset.m_symbol + "\" lists the file \"" + filename
+                + "\", which does not exist (resolved to \"" + pathname.string() + "\")",
+                klammerset.m_loc);
+        }
+        pathname = fs::canonical(pathname);
+        m_state.add_search_dir(pathname.parent_path().string());
+        std::string text = trim_right(string_from_file(pathname.string()));
+        katom_list ks = katomize(line_split(text), pathname);
+        process_katoms(ks, pathname);
+        loaded.insert(loaded.end(), ks.begin(), ks.end());
+    }
+    m_katoms.insert(insert_at, loaded.begin(), loaded.end());
+}
+
 void Machine::extract_klammer_definitions(katom_list katoms)
 {
     fmsg() << katoms << "\n";
@@ -489,12 +549,12 @@ katom_list Machine::apply_klammer(
     return result;
 }
 
-void Machine::apply_klammer_set(
-    Klammer_set& klammer_set, katom_list& katoms, const std::string& target, katom_iter begin, katom_iter end)
+void Machine::apply_klammer_registry(
+    Klammer_registry& klammer_registry, katom_list& katoms, const std::string& target, katom_iter begin, katom_iter end)
 {
     (void)K::log(3, "Klammer");
     std::string name = trim_char(begin->m_text, '@');
-    katom_list applied_katoms = apply_klammer(klammer_set.m_klammers[name], target, begin, end);
+    katom_list applied_katoms = apply_klammer(klammer_registry.m_klammers[name], target, begin, end);
     for (auto& k : applied_katoms) {
         if (k.m_type == katom_t::bar || k.m_type == katom_t::double_bar || k.m_type == katom_t::option_name) {
             k.m_type = katom_t::text;
@@ -504,16 +564,16 @@ void Machine::apply_klammer_set(
 }
 
 void Machine::apply(
-    Klammer_set& klammer_set, katom_list& katoms, const std::string& target)
+    Klammer_registry& klammer_registry, katom_list& katoms, const std::string& target)
 {
-    (void)K::log(3, "Klammer_set");
+    (void)K::log(3, "Klammer_registry");
     for (const auto& [op, cl] : find_spans(
              katoms, begin_klammer_apply, end_klammer_apply, true, command_name)) {
         auto [begin, end] = find_span_katoms(katoms, op, cl);
-        klammer_set.check_klammer(
+        klammer_registry.check_klammer(
             klammer_name_from_katom(begin->m_text, begin->m_loc),
             target, begin->m_loc);
-        apply_klammer_set(klammer_set, katoms, target, begin, end);
+        apply_klammer_registry(klammer_registry, katoms, target, begin, end);
     }
 }
 
diff --git a/mac/machine.h b/mac/machine.h
index 3e938d2..e26d8ad 100644
--- a/mac/machine.h
+++ b/mac/machine.h
@@ -4,9 +4,10 @@
 
 // #include "source.h"
 #include "katom_list.h"
-#include "klammer_set.h"
-#include "target_set.h"
-#include "argtype_set.h"
+#include "klammer_registry.h"
+#include "klammerset_registry.h"
+#include "target_registry.h"
+#include "argtype_registry.h"
 #include "state.h"
 
 #include "error.h"
@@ -20,11 +21,12 @@ public:
     Machine();
 
     // Copy constructor
-    Machine(const Machine& other) 
+    Machine(const Machine& other)
         : m_argtypes(other.m_argtypes)
         , m_state(other.m_state)
         , m_targets(other.m_targets)
         , m_klammers(other.m_klammers)
+        , m_klammersets(other.m_klammersets)
         , m_result(other.m_result)
     {}
 
@@ -35,6 +37,7 @@ public:
             m_state = other.m_state;
             m_targets = other.m_targets;
             m_klammers = other.m_klammers;
+            m_klammersets = other.m_klammersets;
             m_result = other.m_result;
         }
         return *this;
@@ -65,6 +68,7 @@ public:
         bool klammers=true, bool eval=true, bool cond=true, bool read=true);
 
     void expand_constant_klammers(katom_list& katoms, const Katom& op, const Katom& cl);
+    void load_klammerset_files(const Klammerset& klammerset, katom_iter insert_at);
     void extract_machine_definitions();
     void extract_klammer_definitions();
     void extract_klammer_definitions(katom_list katoms);
@@ -72,18 +76,19 @@ public:
 
     katom_list apply_klammer(Klammer& klammer, const std::string& target, katom_iter arguments_begin, katom_iter arguments_end);
 
-    void apply_klammer_set(Klammer_set& klammer_set,
+    void apply_klammer_registry(Klammer_registry& klammer_registry,
                katom_list& katoms, const std::string& target, katom_iter begin, katom_iter end);
 
-    void apply(Klammer_set& klammer_set, katom_list& katoms, const std::string& target);
+    void apply(Klammer_registry& klammer_registry, katom_list& katoms, const std::string& target);
 
     std::string run_phase_functions();
     std::string apply(const std::string& target_name, bool final_processing=true, bool escape_characters=true);
 
-    Argtype_set m_argtypes {};
+    Argtype_registry m_argtypes {};
     State m_state {};
-    Target_set m_targets {};
-    Klammer_set m_klammers {};
+    Target_registry m_targets {};
+    Klammer_registry m_klammers {};
+    Klammerset_registry m_klammersets {};
     input_sources_t m_sources {};
     std::string m_result {};
     std::vector<Katom> m_katoms {};
diff --git a/mac/show.cpp b/mac/show.cpp
index ab27a16..2b6e405 100644
--- a/mac/show.cpp
+++ b/mac/show.cpp
@@ -461,12 +461,12 @@ std::ostream& operator<<(std::ostream& os, const Klammer::components& kc)
 }
 
 
-// Klammer_set
+// Klammer_registry
 
-std::ostream& operator<<(std::ostream& os, const Klammer_set& ks)
+std::ostream& operator<<(std::ostream& os, const Klammer_registry& ks)
 {
-    for (auto klam : ks.m_klammers) {
-        for (auto [k,v] : klam.second.m_defloc) {
+    for (const auto& klam : ks.m_klammers) {
+        for (const auto& [k,v] : klam.second.m_defloc) {
            os << "  " << k << sp_arrow << v << "\n";
         }
         //klam.second.m_defloc.str() << "\n";
@@ -485,30 +485,62 @@ void show_arrow_pair(std::ostream& os, std::pair<std::string,std::string> transf
 std::ostream& operator<<(std::ostream& os, const Target& t)
 {
     os << "<\U0001D517" << broken_bar << t.m_name << broken_bar << t.m_desc << broken_bar;
-    for (auto i : t.m_includes) {
+    for (const auto& i : t.m_includes) {
         os << i << right_arrow << t.m_name << broken_bar;
     }
-    for (auto p : t.m_provides) {
+    for (const auto& p : t.m_provides) {
         os << t.m_name << right_arrow << p << broken_bar;
     }
     os << ">";
     return os;
 }
 
-// Target_set
+// Target_registry
 
-std::ostream& operator<<(std::ostream& os, const Target_set& ts)
+std::ostream& operator<<(std::ostream& os, const Target_registry& ts)
 {
     size_t width = 0;
-    for (auto t : ts.m_targets) {
+    for (const auto& t : ts.m_targets) {
         width = std::max(width, t.first.size());
     }
-    for (auto [name, target] : ts.m_targets) {
+    for (const auto& [name, target] : ts.m_targets) {
         os << std::setw(width) << name << sp_arrow << target << "\n";
     }
     return os;
 }
 
+// Klammerset
+
+std::ostream& operator<<(std::ostream& os, const Klammerset& ks)
+{
+    os << "<\U0001D516" << broken_bar << ks.m_symbol << broken_bar << ks.m_desc;
+    if (!ks.m_date.empty()) {
+        os << broken_bar << ks.m_date;
+    }
+    if (!ks.m_requires.empty()) {
+        os << broken_bar << "requires " << join(ks.m_requires, " / ");
+    }
+    if (!ks.m_files.empty()) {
+        os << broken_bar << join(ks.m_files, " / ");
+    }
+    os << ">";
+    return os;
+}
+
+// Klammerset_registry
+
+std::ostream& operator<<(std::ostream& os, const Klammerset_registry& kr)
+{
+    size_t width = 0;
+    for (const auto& k : kr.m_klammersets) {
+        width = std::max(width, k.first.size());
+    }
+    for (const auto& [symbol, klammerset] : kr.m_klammersets) {
+        os << std::setw(width) << symbol << sp_arrow << klammerset << "\n";
+    }
+    return os;
+}
+
 // Machine 
 
 
@@ -537,6 +569,7 @@ std::ostream& operator<<(std::ostream& os, const Machine& m)
     std::string argtypes_desc = m.m_argtypes.describe(false, 8);
     std::string state_desc = m.m_state.describe(false, 3);
     std::string targets_desc = m.m_targets.describe(4);
+    std::string klammersets_desc = m.m_klammersets.describe(4);
     std::string klammer_desc = m.m_klammers.describe(2);
     std::string source_desc = describe_sources(m);
 
@@ -544,12 +577,13 @@ std::ostream& operator<<(std::ostream& os, const Machine& m)
        << label("Sources", m.m_sources.size()) << source_desc << "\n"
        << label("Argtypes", m.m_argtypes.m_names.size()) << argtypes_desc << "\n"
        << label("Targets", m.m_targets.m_names.size()) << targets_desc << "\n"
+       << label("Klammersets", m.m_klammersets.m_symbols.size()) << klammersets_desc << "\n"
        << label("Klammers", m.m_klammers.m_klammers.size()) << klammer_desc << "\n"
-       << label("State", m.m_state.m_frames.size()) << state_desc; 
+       << label("State", m.m_state.m_frames.size()) << state_desc;
     return os;
 }
 
-void modify_stream(std::string name)
+void modify_stream(const std::string& name)
 {
     if (name == "all") std::cout << kall;
     if (name == "type") std::cout << ktype;
diff --git a/mac/show.h b/mac/show.h
index c1e01c1..d5cbee5 100644
--- a/mac/show.h
+++ b/mac/show.h
@@ -8,9 +8,10 @@
 #include "argtype.h"
 #include "argument.h"
 #include "klammer.h"
-#include "klammer_set.h"
+#include "klammer_registry.h"
+#include "klammerset_registry.h"
 #include "state.h"
-#include "target_set.h"
+#include "target_registry.h"
 #include "machine.h"
 #include "file.h"
 
@@ -143,16 +144,22 @@ std::ostream& operator<<(std::ostream& os, const Klammer::variable_map_t& vm);
 // Klammer::components
 std::ostream& operator<<(std::ostream& os, const Klammer::components& kc);
 
-// Klammer_set
-std::ostream& operator<<(std::ostream& os, const Klammer_set& ks);
+// Klammer_registry
+std::ostream& operator<<(std::ostream& os, const Klammer_registry& ks);
 
 // Target
 std::ostream& operator<<(std::ostream& os, const Target& t);
 
-// Target_set
-std::ostream& operator<<(std::ostream& os, const Target_set& ts);
+// Target_registry
+std::ostream& operator<<(std::ostream& os, const Target_registry& ts);
+
+// Klammerset
+std::ostream& operator<<(std::ostream& os, const Klammerset& ks);
+
+// Klammerset_registry
+std::ostream& operator<<(std::ostream& os, const Klammerset_registry& kr);
 
 // Machine
 std::ostream& operator<<(std::ostream& os, const Machine& m);
 
-void modify_stream(std::string name);
+void modify_stream(const std::string& name);
diff --git a/mac/state.cpp b/mac/state.cpp
index 6023567..c8e2be6 100644
--- a/mac/state.cpp
+++ b/mac/state.cpp
@@ -10,7 +10,7 @@
 
 int State::class_id = 0;
 
-bool Var::defined()
+bool Var::defined() const
 {
     return !m_name.empty();
 }
@@ -24,18 +24,19 @@ std::vector<std::string> Frame::names() const
     return result;
 }
 
-void Frame::set(std::string name, std::string value,
-                std::string delim, std::string desc, Locator loc, Argtype argtype)
+void Frame::set(const std::string& name, const std::string& value,
+                const std::string& delim, const std::string& desc, const Locator& loc,
+                const Argtype& argtype)
 {
     Var v(name, value, delim, desc, loc, argtype);
     m_vars[name] = v;
 }
 
-std::pair<Var, bool> Frame::get(std::string name)
+std::pair<Var, bool> Frame::get(const std::string& name) const
 {
     std::pair<Var, bool> result {Var(), false};
     if (m_vars.contains(name)) {
-        result = {m_vars[name], true};
+        result = {m_vars.at(name), true};
     }
     return result;
 }
@@ -43,7 +44,7 @@ std::pair<Var, bool> Frame::get(std::string name)
 // State
 
 
-void State::open_frame(std::string name)
+void State::open_frame(const std::string& name)
 {
     Frame f(name);
     // m_frames.push_back(f);
@@ -58,19 +59,20 @@ void State::close_frame()
     }
     // Preserve altered machine state:
     string_map machine_state {};
-    for (auto [name, var] : m_frames[0].m_vars) {
+    for (const auto& [name, var] : m_frames[0].m_vars) {
         if (contains(name, "K_")) {
             machine_state[name] = var.m_value;
         }
     }
     m_frames.erase(m_frames.begin());
-    for (auto [name, value] : machine_state) {
+    for (const auto& [name, value] : machine_state) {
         set(name, value, true);
     }
 }
 
-void State::set(std::string name, std::string value, bool update,
-                std::string delim, std::string desc, Locator loc, Argtype argtype)
+void State::set(const std::string& name, const std::string& value, bool update,
+                const std::string& delim, const std::string& desc, const Locator& loc,
+                const Argtype& argtype)
 {
     if (m_frames.empty()) {
         std::stringstream ss {};
@@ -89,9 +91,9 @@ void State::set(std::string name, std::string value, bool update,
     m_frames[0].set(name, value, delim, desc, loc, argtype);
 }
 
-void State::set(std::map<std::string, std::string> varmap)
+void State::set(const std::map<std::string, std::string>& varmap)
 {
-    for (auto [k, v] : varmap) {
+    for (const auto& [k, v] : varmap) {
         set(k, v);
     }
 }
@@ -107,7 +109,7 @@ void State::set(const std::map<std::string, std::string>& varmap,
 }
 
 
-void State::replace(std::string name, std::string value, bool error_if_not_defined)
+void State::replace(const std::string& name, const std::string& value, bool error_if_not_defined)
 {
     if (error_if_not_defined && !get(name).defined()) {
         std::stringstream ss {};
@@ -120,14 +122,14 @@ void State::replace(std::string name, std::string value, bool error_if_not_defin
 void State::add_environment_frame()
 {
     open_frame(klammerstate::shell_environment_name);
-    for (auto [name, value] : environment_variables()) {
+    for (const auto& [name, value] : environment_variables()) {
         set(name, value);
     }
 }
 
-Var State::get(std::string name, bool error_if_not_defined, Locator loc)
+Var State::get(const std::string& name, bool error_if_not_defined, const Locator& loc) const
 {
-    for (auto f : m_frames) {
+    for (const auto& f : m_frames) {
         auto [result, found] = f.get(name);
         if (found) {
             return result;
@@ -141,12 +143,12 @@ Var State::get(std::string name, bool error_if_not_defined, Locator loc)
     }
 }
 
-std::string State::value(std::string name, bool error_if_not_defined, Locator loc)
+std::string State::value(const std::string& name, bool error_if_not_defined, const Locator& loc) const
 {
     return get(name, error_if_not_defined, loc).m_value;
 }
 
-std::string State::subst(std::string text, bool quote_values)
+std::string State::subst(const std::string& text, bool quote_values) const
 {
     (void)K::log(3);
     std::string result = text;
@@ -198,7 +200,8 @@ void State::subst(katom_iter begin, katom_iter end)
 }
 
 void prohibit_change_of_description(
-    std::string name, bool defined, std::string old_desc, std::string new_desc, Locator old_loc, Locator loc)
+    const std::string& name, bool defined, const std::string& old_desc,
+    const std::string& new_desc, const Locator& old_loc, const Locator& loc)
 {
     if (defined && !old_desc.empty() && !new_desc.empty()) {
         std::stringstream ss {};
@@ -216,7 +219,7 @@ void prohibit_change_of_description(
 
 // Parameter_set m_parameters = Parameter_set("name :value :append :replace :delim :desc");
 
-void State::parse_state_katoms(katom_iter begin, katom_iter end, katom_list katoms)
+void State::parse_state_katoms(katom_iter begin, katom_iter end, katom_list& katoms)
 {
     (void)K::log(3, *begin, *(end-1));
     // std::cout << "parse_katoms: " << std::pair(begin + 1, end - 1) << "\n";
@@ -246,11 +249,11 @@ void State::parse_state_katoms(katom_iter begin, katom_iter end, katom_list kato
     ignore_whitespace(next_iter, katoms);
 }
 
-std::vector<std::string> State::all_names()
+std::vector<std::string> State::all_names() const
 {
     std::vector<std::string> result {};
-    for (Frame f : m_frames) {
-        for (auto [name, var] : f.m_vars) {
+    for (const Frame& f : m_frames) {
+        for (const auto& [name, var] : f.m_vars) {
             // std::cout << "Name: " << name << "\n";
             result.push_back(name);
         }
@@ -282,7 +285,7 @@ std::string State::python_code()
     // the file whose @eval names it is found regardless of the cwd.
     python_dirs.insert(python_dirs.end(),
                        m_search_dirs.begin(), m_search_dirs.end());
-    for (auto d : python_dirs) {
+    for (const auto& d : python_dirs) {
         auto python_files = pathnames_with_extension(d, "py");
         if (!python_files.empty()) {
             ss << "sys.path.append('" << d << "')\n";
@@ -308,12 +311,12 @@ std::string State::describe(bool show_environment, int margin_size) const
     std::string margin(margin_size, ' ');
     int i = m_frames.size() - 1;
     std::stringstream ss {};
-    for (auto f : m_frames) {
+    for (const auto& f : m_frames) {
         int width = max_key_length(f.m_vars);
         ss << margin << "Frame " << i-- << ": " << f.m_name << "\n";
         if ((f.m_name != klammerstate::shell_environment_name) ||
             (show_environment && f.m_name == klammerstate::shell_environment_name)) {
-            for (auto [key, value] : f.m_vars) {
+            for (const auto& [key, value] : f.m_vars) {
                 std::string print_value = value.m_value;
                 if (print_value == klammerstate::no_value) {
                     print_value = "<no-value>";
diff --git a/mac/state.h b/mac/state.h
index 2d17e0c..cf0ebdb 100644
--- a/mac/state.h
+++ b/mac/state.h
@@ -14,9 +14,9 @@ class Var
 {
 public:
     Var() = default;
-    Var(std::string name, std::string value=klammerstate::no_value,
-        std::string delim=":", std::string desc="", Locator loc=Locator(),
-        Argtype argtype=Argtype())
+    Var(const std::string& name, const std::string& value=klammerstate::no_value,
+        const std::string& delim=":", const std::string& desc="", const Locator& loc=Locator(),
+        const Argtype& argtype=Argtype())
         : m_name(name)
         , m_value(value)
         , m_delim(delim)
@@ -24,7 +24,7 @@ public:
         , m_loc(loc)
         , m_argtype(argtype)
         {};
-    bool defined();
+    bool defined() const;
 
     std::string m_name {};
     std::string m_value {};
@@ -41,15 +41,15 @@ inline std::string shell_environment_name = "Shell environment";
 class Frame
 {
 public:
-    Frame(std::string name)
+    Frame(const std::string& name)
         : m_name(name)
         {};
 
     std::vector<std::string> names() const;
-    void set(std::string name, std::string value,
-             std::string delim=":", std::string desc="", Locator loc=Locator(),
-             Argtype argtype=Argtype());
-    std::pair<Var, bool> get(std::string name);
+    void set(const std::string& name, const std::string& value,
+             const std::string& delim=":", const std::string& desc="", const Locator& loc=Locator(),
+             const Argtype& argtype=Argtype());
+    std::pair<Var, bool> get(const std::string& name) const;
 
     std::string m_name {};
     std::map<std::string, Var> m_vars {};
@@ -59,24 +59,24 @@ class State
 {
 public:
     static int class_id;
-    void open_frame(std::string name);
+    void open_frame(const std::string& name);
     void close_frame();
-    void set(std::string name, std::string value, bool update=false,
-             std::string delim=" ", std::string desc="", Locator loc=Locator(),
-             Argtype argtype=Argtype());
-    void set(std::map<std::string, std::string> varmap);
+    void set(const std::string& name, const std::string& value, bool update=false,
+             const std::string& delim=" ", const std::string& desc="", const Locator& loc=Locator(),
+             const Argtype& argtype=Argtype());
+    void set(const std::map<std::string, std::string>& varmap);
     void set(const std::map<std::string, std::string>& varmap,
              const Parameter_set& parameters);
-    void replace(std::string name, std::string value, bool error_if_not_defined=true);
+    void replace(const std::string& name, const std::string& value, bool error_if_not_defined=true);
     void add_environment_frame();
-    Var get(std::string name, bool error_if_not_defined=false, Locator loc=Locator());
-    std::string value(std::string name, bool error_if_not_defined=true, Locator loc=Locator());
+    Var get(const std::string& name, bool error_if_not_defined=false, const Locator& loc=Locator()) const;
+    std::string value(const std::string& name, bool error_if_not_defined=true, const Locator& loc=Locator()) const;
 
-    std::string subst(std::string text, bool quote_values=false);
+    std::string subst(const std::string& text, bool quote_values=false) const;
     void subst(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end);
 
-    void parse_state_katoms(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, katom_list katoms);
-    std::vector<std::string> all_names();
+    void parse_state_katoms(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, katom_list& katoms);
+    std::vector<std::string> all_names() const;
     void add_search_dir(const std::string& dir);
     std::string python_code();
     std::string describe(bool show_environment=false, int margin_size=2) const;
diff --git a/mac/target.cpp b/mac/target.cpp
index ea70a49..959c555 100644
--- a/mac/target.cpp
+++ b/mac/target.cpp
@@ -7,32 +7,32 @@
 //#include "text.h"
 #include "util.h"
 
-void Target::add_transform(std::string original, std::string transformed)
+void Target::add_transform(const std::string& original, const std::string& transformed)
 {
     m_transforms.push_back({original, transformed});
 }
 
-void Target::add_transforms(std::string transforms)
+void Target::add_transforms(const std::string& transforms)
 {
     add_transforms(parse_transforms(transforms));
 }
 
-void Target::add_transforms(string_pairs transforms)
+void Target::add_transforms(const string_pairs& transforms)
 {
-    for (auto [old_str, new_str] : transforms) {
+    for (const auto& [old_str, new_str] : transforms) {
         add_transform(old_str, new_str);
     }
 }
 
-void Target::transform(katom_list& katoms)
+void Target::transform(katom_list& katoms) const
 {
     (void)K::log(3);
     std::for_each(
-        katoms.begin(), katoms.end(), 
-        [this] (Katom& k) {       
+        katoms.begin(), katoms.end(),
+        [this] (Katom& k) {
             // std::cout << "transform: " << k << "\n";
             if (k.m_type != katom_t::literal) {
-                for (auto [a, b] : this->m_transforms) {
+                for (const auto& [a, b] : this->m_transforms) {
                     // std::cout << "  " << a << right_arrow << b << "\n";
                     k.m_text = string_replace(k.m_text, a, b);
                 }
@@ -41,7 +41,7 @@ void Target::transform(katom_list& katoms)
 }
 
 std::vector<std::pair<std::string, std::string>>
-parse_transforms(std::string transform_string)
+parse_transforms(const std::string& transform_string)
 {
     (void)K::log(3);
     if (trim(transform_string).empty()) return {};
@@ -59,7 +59,7 @@ parse_transforms(std::string transform_string)
     return result;
 }
 
-void Target::add_escapes(std::string escape_spec)
+void Target::add_escapes(const std::string& escape_spec)
 {
     auto words = word_split(escape_spec);
     for (size_t i = 0; i + 1 < words.size(); i += 2) {
@@ -142,9 +142,9 @@ std::string hide_structural_characters(const std::string& s)
     return result;
 }
 
-void Target::add_after_apply(std::string function_specs)
+void Target::add_after_apply(const std::string& function_specs)
 {
-    for (auto f : regex_split(function_specs, std::regex(R"(\s+;\s+)"), true)) {
+    for (const auto& f : regex_split(function_specs, std::regex(R"(\s+;\s+)"), true)) {
         // msg() << "Add " << m_name << " after-apply: " << f << "\n";
         m_after_apply.push_back(f);
     }
diff --git a/mac/target.h b/mac/target.h
index 3d1e4fe..f91041b 100644
--- a/mac/target.h
+++ b/mac/target.h
@@ -11,25 +11,25 @@ class Target
 {
 public:
     Target() = default;
-//    Target(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, Argtype_set argtypes);
-    Target(std::string name, std::string desc, Locator loc)
+//    Target(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, Argtype_registry argtypes);
+    Target(const std::string& name, const std::string& desc, const Locator& loc)
         : m_name(name)
         , m_desc(desc)
         , m_loc(loc)
         {};
 
-    void add_transform(std::string original, std::string transformed);
-    void add_transforms(std::string transforms);
-    void add_transforms(std::vector<std::pair<std::string, std::string>> transforms);
-    void transform(std::vector<Katom>& katoms);
+    void add_transform(const std::string& original, const std::string& transformed);
+    void add_transforms(const std::string& transforms);
+    void add_transforms(const std::vector<std::pair<std::string, std::string>>& transforms);
+    void transform(std::vector<Katom>& katoms) const;
 
-    void add_escapes(std::string escape_spec);
+    void add_escapes(const std::string& escape_spec);
     std::string escape_text(std::string text) const;
     std::string unescape_text(std::string text) const;
     std::string resolve_escapes(std::string text) const;
     static std::string escape_marker(const std::string& ch);
 
-    void add_after_apply(std::string function_specs);
+    void add_after_apply(const std::string& function_specs);
 
     std::string m_name {};
     std::string m_desc {};
@@ -40,13 +40,13 @@ public:
     Locator m_loc {};
     std::vector<std::pair<std::string, std::string>> m_transforms {};
     std::vector<std::pair<std::string, std::string>> m_escapes {};
-//    Argtype_set m_argtypes {};
+//    Argtype_registry m_argtypes {};
 
 
 };
 
 std::vector<std::pair<std::string, std::string>>
-parse_transforms(std::string transform_string);
+parse_transforms(const std::string& transform_string);
 
 // Decode every KTESC<hex>KTESC marker in text back to its original
 // characters.  Used for the final output (after target-declared escapes have
diff --git a/mac/target_set.cpp b/mac/target_registry.cpp
similarity index 67%
rename from mac/target_set.cpp
rename to mac/target_registry.cpp
index 25b8753..093c22c 100644
--- a/mac/target_set.cpp
+++ b/mac/target_registry.cpp
@@ -1,8 +1,7 @@
 #include <sstream>
 #include <iterator>
-#include <algorithm>
 
-#include "target_set.h"
+#include "target_registry.h"
 #include "error.h"
 #include "log.h"
 #include "util.h"
@@ -10,10 +9,10 @@
 #include "log.h"
 #include "katom.h"
 
-std::string Target_set::declare_name = "k";
-std::string Target_set::general_name = "*";
+std::string Target_registry::declare_name = "k";
+std::string Target_registry::general_name = "*";
 
-Target_set::Target_set()
+Target_registry::Target_registry()
         : m_parameters(Parameter_set("name | desc :after_apply :after_write :includes :escape | transforms.rest"))
 {
     Target k(declare_name, "Description of parameters and klammer result", Locator());
@@ -22,16 +21,15 @@ Target_set::Target_set()
     add(general);
 }
 
-void Target_set::add(Target target)
+void Target_registry::add(Target target)
 {
     (void)K::log(3, target);
     check_for_previous_definition(target.m_name, target.m_loc);
     m_targets[target.m_name] = target;
     m_names.push_back(target.m_name);
-    m_descs.push_back(target.m_desc);
 }
 
-void Target_set::add(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms)
+void Target_registry::add(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms)
 {
     (void)K::log(3, *begin, *(end - 1));
     auto [positional, optional, rest] =
@@ -40,14 +38,10 @@ void Target_set::add(std::vector<Katom>::iterator begin, std::vector<Katom>::ite
 
     //std::cout << ktype << "Transformed: " << kreplaced << std::pair(begin, end) << "\n";
     //std::cout << values << "\n";
-    check_for_previous_definition(values["name"], begin->m_loc);
     Target target(values["name"], values["desc"], begin->m_loc);
     target.add_transforms(values["transforms"]);
     target.add_escapes(values["escape"]);
     target.add_after_apply(values["after_apply"]);
-    // for (auto included_target : word_split(values["includes"])) {
-    //    msg() << "Include: " << included_target << "\n";
-    // }
     target.m_includes = word_split(values["includes"]);
     // Inherit escapes from included targets
     for (const auto& included : target.m_includes) {
@@ -57,15 +51,13 @@ void Target_set::add(std::vector<Katom>::iterator begin, std::vector<Katom>::ite
             }
         }
     }
-    m_targets[target.m_name] = target;
-    m_names.push_back(target.m_name);
+    // Registration (and the previous-definition check) goes through
+    // add(Target) -- the single registration path.
+    add(target);
 
-    for (auto [name, defined_target] : m_targets) {
-        // msg() << name << sp_arrow << defined_target << "\n";
+    for (auto& [name, defined_target] : m_targets) {
         if (is_in(name, target.m_includes)) {
             defined_target.m_provides.push_back(target.m_name);
-            // msg() << "  " << name << " provides " << target.m_name << "\n   " << defined_target.m_provides << "\n";
-            m_targets[name] = defined_target;
         }
     }
 
@@ -76,56 +68,62 @@ void Target_set::add(std::vector<Katom>::iterator begin, std::vector<Katom>::ite
 }
 
 
-void Target_set::check_for_previous_definition(std::string name, Locator loc)
+void Target_registry::check_for_previous_definition(const std::string& name, const Locator& loc) const
 {
     if (has(name)) {
-        Target current = m_targets[name];
+        const Target& current = m_targets.at(name);
         throw Target_error("Target \"" + name + "\" is already defined:\n  " + current.m_loc.desc(),
                            loc, false);
     }
 }
 
-bool Target_set::has(std::string target_name)
+bool Target_registry::has(const std::string& target_name) const
 {
-    return std::ranges::find(m_names, target_name) != m_names.end();
+    // Membership comes from the map; m_names exists only to preserve
+    // definition order for describe().
+    return m_targets.count(target_name) > 0;
 }
 
 
-Target Target_set::get(std::string target_name, Locator loc)
+Target Target_registry::get(const std::string& target_name, const Locator& loc) const
 {
-    if (has(target_name) || target_name == Target_set::general_name) {
+    if (has(target_name) || target_name == Target_registry::general_name) {
         return m_targets.at(target_name);
     } else {
         throw Target_error("Target " + target_name + " does not exist", loc);
     }
 }
 
-void Target_set::transform(std::string target_name, katom_list& katoms)
+void Target_registry::transform(const std::string& target_name, katom_list& katoms) const
 {
     (void)K::log(3);
-    m_targets[target_name].transform(katoms);
+    m_targets.at(target_name).transform(katoms);
 }
 
-std::vector<std::string> Target_set::user_defined()
+std::vector<std::string> Target_registry::user_defined() const
 {
     return collect_if(
-        m_names, [](auto name) {
-            return name != Target_set::declare_name && name != Target_set::general_name; });
+        m_names, [](const auto& name) {
+            return name != Target_registry::declare_name && name != Target_registry::general_name; });
 }
 
-std::vector<std::string> Target_set::applicable()
+std::vector<std::string> Target_registry::applicable() const
 {
     return collect_if(
-        m_names, [](auto name) {
-            return name != Target_set::declare_name; });
+        m_names, [](const auto& name) {
+            return name != Target_registry::declare_name; });
 }
 
-std::string Target_set::describe(int margin, bool long_format) const
+std::string Target_registry::describe(int margin, bool long_format) const
 {
     std::string tab(margin, ' ');
     std::stringstream ss {};
+    std::vector<std::string> descs {};
+    for (const std::string& name : m_names) {
+        descs.push_back(m_targets.at(name).m_desc);
+    }
     auto name_width = max_length(m_names);
-    auto desc_width = max_length(m_descs);
+    auto desc_width = max_length(descs);
     for (const std::string& name : m_names) {
         const Target& t = m_targets.at(name);
         if (long_format) {
diff --git a/mac/target_set.h b/mac/target_registry.h
similarity index 77%
rename from mac/target_set.h
rename to mac/target_registry.h
index 364ba9e..58c3ba4 100644
--- a/mac/target_set.h
+++ b/mac/target_registry.h
@@ -6,17 +6,17 @@
 #include "argument_set.h"
 #include "katom.h"
 
-class Target_set
+class Target_registry
 {
 public:
     static std::string declare_name;
     static std::string general_name;
 
-    Target_set();
+    Target_registry();
 
     void add(Target target);
     void add(std::vector<Katom>::iterator begin, std::vector<Katom>::iterator end, std::vector<Katom>& katoms);
-    void check_for_previous_definition(std::string name, Locator loc);
+    void check_for_previous_definition(const std::string& name, const Locator& loc) const;
 
 
     /*
@@ -27,19 +27,18 @@ public:
     */
 
 
-    bool has(std::string target_name);
-    Target get(std::string target_name, Locator loc);
-    void transform(std::string target_name, std::vector<Katom>& katoms);
+    bool has(const std::string& target_name) const;
+    Target get(const std::string& target_name, const Locator& loc) const;
+    void transform(const std::string& target_name, std::vector<Katom>& katoms) const;
 
-    std::vector<std::string> user_defined();
-    std::vector<std::string> applicable();
+    std::vector<std::string> user_defined() const;
+    std::vector<std::string> applicable() const;
 
     std::string describe(int margin=2, bool long_format=false) const;
 
-    //Argtype_set m_argtypes {};
+    //Argtype_registry m_argtypes {};
     std::map<std::string, Target> m_targets {};
     std::vector<std::string> m_names {};
-    std::vector<std::string> m_descs {};
     Parameter_set m_parameters {};
 
 
@@ -51,7 +50,7 @@ public:
 
 
     //Parameter_set m_parameters =
-    //    Parameter_set(katomize({"name :desc | transforms.rest"}, "target_set"));
+    //    Parameter_set(katomize({"name :desc | transforms.rest"}, "target_registry"));
 
     /*
     // Targets(Statevar_set& statevars);
diff --git a/mac/util.cpp b/mac/util.cpp
index 15f1065..aa515e2 100644
--- a/mac/util.cpp
+++ b/mac/util.cpp
@@ -111,7 +111,7 @@ std::string regex_escape(const std::string& s)
     return result;
 }
 
-strings_t regex_split(std::string s, std::regex re, bool trim_parts)
+strings_t regex_split(const std::string& s, const std::regex& re, bool trim_parts)
 {
     strings_t result = {};
     if (s.size() == 0) {
@@ -134,17 +134,17 @@ strings_t word_split(const std::string& s)
     return regex_split(s, std::regex("\\s+"));
 }
 
-bool is_in(std::string s, strings_t v)
+bool is_in(const std::string& s, const strings_t& v)
 {
     return find(v.begin(), v.end(), s) != v.end();
 }
 
-bool is_not_in(std::string s, strings_t v)
+bool is_not_in(const std::string& s, const strings_t& v)
 {
     return find(v.begin(), v.end(), s) == v.end();
 }
 
-strings_t find_all(std::string str, std::regex pattern, int match_group)
+strings_t find_all(const std::string& str, const std::regex& pattern, int match_group)
 {
     std::sregex_iterator end {};
     strings_t result;
@@ -153,7 +153,7 @@ strings_t find_all(std::string str, std::regex pattern, int match_group)
     return result;
 }
 
-strings_t find_all(std::string str, std::string pattern, int match_group)
+strings_t find_all(const std::string& str, const std::string& pattern, int match_group)
 {
     return find_all(str, std::regex(pattern), match_group);
 }
@@ -168,7 +168,7 @@ strings_t split_into_paragraphs(const std::string& s)
 
 }
 
-std::string add_margin(std::string s, unsigned int margin_size)
+std::string add_margin(const std::string& s, unsigned int margin_size)
 {
     auto margin = std::string(margin_size, ' ');
     return trim_right(
@@ -297,7 +297,7 @@ std::string to_be(int count, bool present)
     return result;
 }
 
-int max_length(strings_t ss)
+int max_length(const strings_t& ss)
 {
     size_t result = 0;
     for_each(ss.begin(), ss.end(),
@@ -349,7 +349,7 @@ std::vector<std::pair<std::string, std::string>> environment_variables(bool allo
     return result;
 }
 
-std::string replace_environment_variables(std::string str) 
+std::string replace_environment_variables(const std::string& str)
 {
     if (str.find('{') == std::string::npos || str.find('}') == std::string::npos) {
         return str;
@@ -398,10 +398,10 @@ std::string abbrev(const std::string& s, unsigned int max_length, bool remove_ne
     return result;
 }
 
-void remove_element(std::vector<std::string>& ss, std::string removed)
+void remove_element(std::vector<std::string>& ss, const std::string& removed)
 {
     ss.erase(std::remove_if(ss.begin(), ss.end(), 
-                            [&removed](std::string s) { return s == removed; }),
+                            [&removed](const std::string& s) { return s == removed; }),
              ss.end());
 }
 
@@ -428,7 +428,7 @@ std::string display_string(const std::string& s, unsigned int width, bool replac
     return result;
 }
 
-std::pair<std::string,std::string> extract_parameter_type(std::string parameter_name)
+std::pair<std::string,std::string> extract_parameter_type(const std::string& parameter_name)
 {
     std::regex name_pat { R"((\w+)\.(\w+))" };
     std::smatch match {};
@@ -487,7 +487,8 @@ std::string get_env_var(const std::string& var) {
     return val ? std::string(val) : "";
 }
 
-std::string freplace(const std::string src, std::regex pattern, std::function<std::string(std::smatch)> func)
+std::string freplace(const std::string& src, const std::regex& pattern,
+                     const std::function<std::string(std::smatch)>& func)
 {
     std::string result {};
     std::smatch match;
diff --git a/mac/util.h b/mac/util.h
index 00bdc9c..9cb263c 100644
--- a/mac/util.h
+++ b/mac/util.h
@@ -36,13 +36,13 @@ std::string string_replace(const std::string& source, const std::string& old_str
 std::string regex_escape(const std::string& s);
 bool contains(const std::string& str, const std::string& substr);
 bool contains(const std::vector<std::string>& strings, const std::string& element);
-std::vector<std::string> regex_split(std::string s, std::regex re, bool trim_parts=true);
+std::vector<std::string> regex_split(const std::string& s, const std::regex& re, bool trim_parts=true);
 std::vector<std::string> word_split(const std::string& s);
-bool is_in(std::string s, std::vector<std::string> v);
-bool is_not_in(std::string s, std::vector<std::string> v);
-std::vector<std::string> find_all(std::string str, std::regex pattern, int match_group=0);
-std::vector<std::string> find_all(std::string str, std::string pattern, int match_group=0);
-std::string add_margin(std::string s, unsigned int margin_size);
+bool is_in(const std::string& s, const std::vector<std::string>& v);
+bool is_not_in(const std::string& s, const std::vector<std::string>& v);
+std::vector<std::string> find_all(const std::string& str, const std::regex& pattern, int match_group=0);
+std::vector<std::string> find_all(const std::string& str, const std::string& pattern, int match_group=0);
+std::string add_margin(const std::string& s, unsigned int margin_size);
 std::string justify(const std::string& input_text, unsigned int text_width=80, unsigned int margin_width=0);
 std::string join(const std::vector<std::string>& ss, const std::string& separator = " ");
 std::string join(int argc, char* array[], const std::string& separator = " ");
@@ -50,26 +50,27 @@ std::string argv_to_string(int argc, char* argv[]);
 std::string plural(const std::string& word, int count);
 std::string plural(const std::string& word, const std::vector<std::string>& things);
 std::string to_be(int count, bool present = true);
-int max_length(std::vector<std::string> ss);
+int max_length(const std::vector<std::string>& ss);
 std::vector<std::pair<std::string, std::string>> environment_variables(bool allow_empty_definitions=true);
-std::string replace_environment_variables(std::string str);
+std::string replace_environment_variables(const std::string& str);
 std::string abbrev(const std::string& s, unsigned int max_length=65, bool remove_newlines=true);
-void remove_element(std::vector<std::string>& ss, std::string removed);
+void remove_element(std::vector<std::string>& ss, const std::string& removed);
 void remove_duplicates(std::vector<std::string>& ss);
 std::string display_string(const std::string& s, unsigned int width=40, bool replace_newlines=true);
-std::pair<std::string,std::string> extract_parameter_type(std::string parameter_name);
+std::pair<std::string,std::string> extract_parameter_type(const std::string& parameter_name);
 std::tuple<std::string, std::string, bool> regex_split_prefix(const std::regex& pattern, const std::string& text);
 std::vector<std::string> dlist_split(const std::string& s);
 std::string get_env_var(const std::string& var);
-std::string freplace(const std::string src, std::regex pattern, std::function<std::string(std::smatch)> func);
+std::string freplace(const std::string& src, const std::regex& pattern,
+                     const std::function<std::string(std::smatch)>& func);
 std::string exec(const char* cmd);
 
-inline std::string q_(std::string s)
+inline std::string q_(const std::string& s)
 {
     return "\"" + s + "\"";
 }
 
-inline std::string qq_(std::string s)
+inline std::string qq_(const std::string& s)
 {
     if (s.find('\n') == std::string::npos) {
         return "\"" + s + "\"";
@@ -97,7 +98,7 @@ bool all_equal(const std::vector<T>& v) {
 }
 
 template <typename T>
-int max_key_length(std::map<std::string, T> map)
+int max_key_length(const std::map<std::string, T>& map)
 {
     size_t result = 0;
     for_each(map.begin(), map.end(),
diff --git a/sks/document/document_class.cpp b/sks/document/document_class.cpp
index aed9cad..29561cc 100644
--- a/sks/document/document_class.cpp
+++ b/sks/document/document_class.cpp
@@ -11,7 +11,7 @@
 #include "log.h"
 #include "file.h"
 
-bool strbool(std::string s, Locator loc)
+bool strbool(const std::string& s, const Locator& loc)
 {
     std::vector<std::string> values = {"false", "False", "0", "true", "True", "1"};
     if (is_not_in(s, values)) {
@@ -136,7 +136,7 @@ void Document_class::save_string_input_as_file()
 }
 
 
-fs::path parse_input_filename(std::string s, std::string input_dir)
+fs::path parse_input_filename(const std::string& s, const std::string& input_dir)
 {
     fs::path p(s);
     if (p.extension() != ".kt") {
@@ -160,13 +160,13 @@ fs::path parse_input_filename(std::string s, std::string input_dir)
     return p;
 }
 
-void Document_class::write(std::string filename, std::string contents)
+void Document_class::write(const std::string& filename, const std::string& contents)
 {
     write_file(filename, contents, write_files);
 }
 
 
-void write_file(std::string filename, std::string contents, bool write_p)
+void write_file(const std::string& filename, const std::string& contents, bool write_p)
 {
     if (write_p) {
         string_to_file(filename, contents);
@@ -177,14 +177,14 @@ void write_file(std::string filename, std::string contents, bool write_p)
 
 
 /*
-void output_msg(std::string msg)
+void output_msg(const std::string& msg)
 {
     std::cout << red;
     (void)K::log(1, msg);
     std::cout << black;
 }    
 
-void Document_class::create_directory(std::string directory)
+void Document_class::create_directory(const std::string& directory)
 {
     if (write_files) {
         fs::create_directories(directory);
diff --git a/sks/document/document_class.h b/sks/document/document_class.h
index a163e18..3d795fa 100644
--- a/sks/document/document_class.h
+++ b/sks/document/document_class.h
@@ -16,7 +16,7 @@ inline std::map<std::string, int> html_tags {
 
 using string_pairs_t = std::vector<std::pair<std::string,std::string>>;
 
-std::string unescape_newlines(std::string s);
+std::string unescape_newlines(const std::string& s);
 
 enum class docstruct_t {
     plain,
@@ -24,7 +24,7 @@ enum class docstruct_t {
     book
 };
 
-inline docstruct_t docstruct(std::string name)
+inline docstruct_t docstruct(const std::string& name)
 {
     if (name == "plain") {
         return docstruct_t::plain;
@@ -43,41 +43,41 @@ public:
     void save_string_input_as_file();
 
     //void create_directory(std::string directory);
-    void write(std::string filename, std::string contents);
+    void write(const std::string& filename, const std::string& contents);
 
     /*
     strings_t get_css_files(
-        std::string output_dir,
-        std::string css_text, strings_t css_files, bool write_file);
+        const std::string& output_dir,
+        const std::string& css_text, const strings_t& css_files, bool write_file);
     */
 
     strings_t get_js_files(
         bool nav, bool include_sks_js,
-        std::string pages_basenames_filename); // , std::string output_dir, bool write_file);
+        const std::string& pages_basenames_filename); // , const std::string& output_dir, bool write_file);
 
     argmap m_args {};
-    void write_basenames_js_file(std::string filename, std::vector<std::string> basenames);
+    void write_basenames_js_file(const std::string& filename, const std::vector<std::string>& basenames);
     std::string create_html_output_directories();
     std::string create_tex_output_directories();
 
     std::pair<std::vector<std::string>, std::vector<std::string>> 
-    html_auxiliary_files(std::string output_directory, std::string pages_basename_filename,
-                         std::vector<std::string> custom_css_files);
+    html_auxiliary_files(const std::string& output_directory, const std::string& pages_basename_filename,
+                         const std::vector<std::string>& custom_css_files);
 
 
     void process_input_files();
-    std::vector<Heading> insert_section_numbers(std::string marker="___NUM___", bool add_to_toc=true);
+    std::vector<Heading> insert_section_numbers(const std::string& marker="___NUM___", bool add_to_toc=true);
     void insert_html_caption_numbers();
-    std::vector<std::tuple<std::string, std::string, std::string>> reference_list(std::string target_marker);
+    std::vector<std::tuple<std::string, std::string, std::string>> reference_list(const std::string& target_marker);
     std::map<std::string, std::string> id_to_caption_number();
     std::map<std::string, std::vector<std::pair<std::string, std::string>>> html_references();
     void resolve_html_references();
     std::string single_page_toc();
-    elements_t page(std::string body, std::string output_dir, int max_level);
+    elements_t page(const std::string& body, const std::string& output_dir, int max_level);
 
-    std::string make_single_html_page(std::string output_directory);
+    std::string make_single_html_page(const std::string& output_directory);
     std::string make_html_navigation_structure(
-        std::string output_directory, std::vector<Heading> headings);
+        const std::string& output_directory, std::vector<Heading> headings);
     std::string html();
     std::string tex();
     std::string make_help_page();
@@ -167,13 +167,13 @@ public:
     std::string m_cache_dir {};
 };
 
-fs::path parse_input_filename(std::string s, std::string input_dir);
-void write_file(std::string filename, std::string contents, bool write_files);
+fs::path parse_input_filename(const std::string& s, const std::string& input_dir);
+void write_file(const std::string& filename, const std::string& contents, bool write_files);
 
 /*
 std::vector<std::string> combine_files(
-    std::vector<std::string> filenames, std::string output_filename,
-    std::string prolog="", std::string epilog="",
+    const std::vector<std::string>& filenames, const std::string& output_filename,
+    const std::string& prolog="", const std::string& epilog="",
     bool write_file_p=true,
     std::function <std::string(std::string)> processor=nullptr);
 */
diff --git a/sks/document/document_html.cpp b/sks/document/document_html.cpp
index 62d9155..3525038 100644
--- a/sks/document/document_html.cpp
+++ b/sks/document/document_html.cpp
@@ -10,7 +10,7 @@
 #include "show.h"
 #include "file.h"
 
-std::string unescape_newlines(std::string s)
+std::string unescape_newlines(const std::string& s)
 {
     return string_replace(s, " ___NL___ ", "\n");
 
@@ -44,7 +44,7 @@ std::string insert_missing_ids(std::smatch match)
     return result;
 }
 
-std::string insert_ids(std::string html_text)
+std::string insert_ids(const std::string& html_text)
 {
     (void)K::log(3);
     std::string result = html_text;
@@ -154,7 +154,7 @@ std::string Document_class::font_definitions()
     return ss.str();
 }
 
-void Document_class::write_basenames_js_file(std::string filename, std::vector<std::string> basenames)
+void Document_class::write_basenames_js_file(const std::string& filename, const std::vector<std::string>& basenames)
 {
     (void)K::log(3);
     std::string tab("        ");
@@ -202,7 +202,7 @@ std::string Document_class::create_html_output_directories()
     return output_directory;
 }
 
-strings_t get_css_files(strings_t custom_css_files)
+strings_t get_css_files(const strings_t& custom_css_files)
 {
     (void)K::log(3);
     strings_t result = sks_files_of_type("css");
@@ -223,7 +223,7 @@ std::vector<std::string> js_basenames(bool nav)
 
 strings_t Document_class::get_js_files(
     bool nav, bool include_sks_js,
-    std::string pages_basenames_filename)
+    const std::string& pages_basenames_filename)
 {
     (void)K::log(3);
     strings_t result {};
@@ -244,13 +244,13 @@ strings_t Document_class::get_js_files(
 }
 
 
-strings_t link_filenames(strings_t& full_filenames, std::string page_dir)
+strings_t link_filenames(strings_t& full_filenames, const std::string& page_dir)
 {
     strings_t result {};
     fs::path page_dir_path(page_dir);
     // int i = 0;
     std::transform(full_filenames.begin(), full_filenames.end(), std::back_inserter(result),
-                   [&](std::string f) {
+                   [&](const std::string& f) {
                        fs::path full(f);
                        //msg() << i << full << " " << full.filename() << "\n";
                        fs::path path(page_dir_path / full.filename());
@@ -260,8 +260,8 @@ strings_t link_filenames(strings_t& full_filenames, std::string page_dir)
 }
 
 std::pair<std::vector<std::string>, std::vector<std::string>>
-Document_class::html_auxiliary_files(std::string output_directory, std::string pages_basenames_filename,
-                                     std::vector<std::string> custom_css_files)
+Document_class::html_auxiliary_files(const std::string& output_directory, const std::string& pages_basenames_filename,
+                                     const std::vector<std::string>& custom_css_files)
 {
     (void)K::log(3);
     strings_t all_css_files = custom_css_files;
@@ -352,7 +352,7 @@ std::string increment_level(int level, std::vector<int> &levels)
 }
 
 
-std::string extract_id(std::string attr)
+std::string extract_id(const std::string& attr)
 {
     std::smatch match {};
     if (!std::regex_match(attr, match, id_attr_rgx)) {
@@ -362,7 +362,7 @@ std::string extract_id(std::string attr)
 }
 
 std::vector<Heading>
-Document_class::insert_section_numbers(std::string marker, bool add_to_toc)
+Document_class::insert_section_numbers(const std::string& marker, bool add_to_toc)
 {
     std::vector<int> levels(9, 0);
     std::smatch match {};
@@ -407,7 +407,7 @@ Document_class::insert_section_numbers(std::string marker, bool add_to_toc)
     return headings;
 }    
 
-int get_caption_number(std::map<std::string, int>& numbers, std::string label)
+int get_caption_number(std::map<std::string, int>& numbers, const std::string& label)
 {
     int result;
     if (numbers.count(label) == 0) {
@@ -470,7 +470,7 @@ void Document_class::insert_html_caption_numbers()
 
 
 std::vector<std::tuple<std::string, std::string, std::string>>
-Document_class::reference_list(std::string target_marker)
+Document_class::reference_list(const std::string& target_marker)
 {
     std::regex reference_rgx("__REF__");
     std::regex target_rgx("<div id=\"(.*?)\" data-label=\"(.*?)\" class=\"caption_");
@@ -519,7 +519,7 @@ std::map<std::string, std::string> Document_class::id_to_caption_number()
 }
     
 
-std::pair<int, int> offset_spec_to_count(std::string spec)
+std::pair<int, int> offset_spec_to_count(const std::string& spec)
 {
     std::regex rgx(R"((\w+)\s*(\d*))");
     std::smatch match {};
@@ -637,7 +637,7 @@ std::string Document_class::single_page_toc()
 }
 
 
-elements_t Document_class::page(std::string body_text, std::string output_dir, int max_level)
+elements_t Document_class::page(const std::string& body_text, const std::string& output_dir, int max_level)
 {
     (void)K::log(3);
     std::string toc {}; // Calculate
@@ -674,7 +674,7 @@ elements_t Document_class::page(std::string body_text, std::string output_dir, i
     return page;
 }
 
-std::string Document_class::make_single_html_page(std::string output_directory)
+std::string Document_class::make_single_html_page(const std::string& output_directory)
 {
     (void)K::log(3);
     std::stringstream ss {};;
@@ -694,7 +694,7 @@ std::string Document_class::make_single_html_page(std::string output_directory)
 }
 
 std::string Document_class::make_html_navigation_structure(
-    std::string output_directory, std::vector<Heading> headings)
+    const std::string& output_directory, std::vector<Heading> headings)
 {
     msg() << "Navigation format\n";
     std::vector<std::string> pages_basenames {};
diff --git a/sks/document/heading.cpp b/sks/document/heading.cpp
index 0e9dfd3..79507d7 100644
--- a/sks/document/heading.cpp
+++ b/sks/document/heading.cpp
@@ -40,7 +40,7 @@ int unnumbered_id = 0;
 
 /*
 std::tuple<std::string, std::vector<Heading>, std::vector<unsigned int>, unsigned int>
-add_section_numbers(std::string s, std::string basename, std::vector<unsigned int> levels, unsigned int initial_id,
+add_section_numbers(const std::string& s, const std::string& basename, std::vector<unsigned int> levels, unsigned int initial_id,
                     std::map<std::string, std::string>& section_id_map)
 {
     (void)K::log(3);
@@ -155,7 +155,7 @@ std::string make_html_table_of_contents(std::vector<Heading> headings)
 }
 
 std::string toc_link_attrs(
-    std::string section, std::string title, std::string filename, std::string target, int level)
+    const std::string& section, const std::string& title, const std::string& filename, const std::string& target, int level)
 {
     std::string basename = file_basename(filename);
     std::stringstream ss {};
@@ -259,7 +259,7 @@ make_navigation_table_of_contents(std::vector<Heading> headings)
 }
 
 void show_table_of_contents(
-    std::string kt_root_filename, std::string title, std::vector<Heading> headings)
+    const std::string& kt_root_filename, const std::string& title, std::vector<Heading> headings)
 {
     long unsigned int width = kt_root_filename.size();
     for (Heading h : headings) {
@@ -285,7 +285,7 @@ void show_table_of_contents(
 }
 
 std::string cache_table_of_contents(
-    std::string kt_root_filename, std::string title, std::vector<Heading> headings)
+    const std::string& kt_root_filename, const std::string& title, std::vector<Heading> headings)
 {
     long unsigned int width = kt_root_filename.size();
     for (Heading h : headings) {
diff --git a/sks/document/heading.h b/sks/document/heading.h
index ee61376..fe64338 100644
--- a/sks/document/heading.h
+++ b/sks/document/heading.h
@@ -8,8 +8,8 @@ const std::string link_delimiter { "%" };
 
 class Heading {
 public:
-    Heading(int level, std::string filename, std::string section, std::string id,
-            std::string number, std::string title)
+    Heading(int level, const std::string& filename, const std::string& section, const std::string& id,
+            const std::string& number, const std::string& title)
         : m_level(level), m_filename(filename), m_section(section), m_id(id),
           m_number(number), m_title(title)
         {};
@@ -25,7 +25,7 @@ std::ostream& operator<<(std::ostream& os, const Heading h);
 
 /*
 std::tuple<std::string, std::vector<Heading>, std::vector<unsigned int>, unsigned int>
-add_section_numbers(std::string s, std::string basename, std::vector<unsigned int> levels, unsigned int initial_id,
+add_section_numbers(const std::string& s, const std::string& basename, std::vector<unsigned int> levels, unsigned int initial_id,
                     std::map<std::string, std::string>& section_id_map);
 */
 
@@ -35,7 +35,7 @@ std::pair<int, std::string>
 make_navigation_table_of_contents(std::vector<Heading> headings);
 
 void show_table_of_contents(
-    std::string kt_filename, std::string title, std::vector<Heading> headings);
+    const std::string& kt_filename, const std::string& title, std::vector<Heading> headings);
 
 std::string cache_table_of_contents(
-    std::string kt_root_filename, std::string title, std::vector<Heading> headings);
+    const std::string& kt_root_filename, const std::string& title, std::vector<Heading> headings);
diff --git a/sks/document/reference.cpp b/sks/document/reference.cpp
index 5eb8008..2147112 100644
--- a/sks/document/reference.cpp
+++ b/sks/document/reference.cpp
@@ -29,7 +29,7 @@ std::ostream& operator<<(std::ostream& os, const numbered_elements& line_states)
     return os;
 }
 
-std::string  add_latex_caption_numbers(std::string latex_text)
+std::string  add_latex_caption_numbers(const std::string& latex_text)
 {
     std::string caption_delimiter { "__CAPTION__" }; // But also in kutil.py
     std::regex caption_delimiter_rgx(caption_delimiter);
@@ -74,7 +74,7 @@ std::string  add_latex_caption_numbers(std::string latex_text)
     return result;
 }
 
-numbered_elements latex_line_states(std::vector<std::string> lines)
+numbered_elements latex_line_states(const std::vector<std::string>& lines)
 {
     // \hypertarget{Reference-Figure-0}{}\label{Label-Reference-Figure-0}
     std::regex element_container_rgx(BS + R"(hypertarget\{(Reference-(\w+)-\d+)\}.*)");
@@ -96,9 +96,9 @@ numbered_elements latex_line_states(std::vector<std::string> lines)
     return states;
 }
 
-std::string find_target(std::string target,
-                        std::vector<std::string>& lines, int start, numbered_elements states,
-                        std::string target_type, int target_count, std::string direction)
+std::string find_target(const std::string& target,
+                        const std::vector<std::string>& lines, int start, const numbered_elements& states,
+                        const std::string& target_type, int target_count, const std::string& direction)
 {
     // msg() << "find_target: " << target_type << " target_count: " << target_count
     //      << " direction: " << direction << "\n";
@@ -137,7 +137,7 @@ std::string find_target(std::string target,
 }
 
 std::string resolve_caption_references(
-    std::string target, std::vector<std::string> lines, numbered_elements states)
+    const std::string& target, const std::vector<std::string>& lines, numbered_elements states)
 {
     //auto lines = regex_split(text, std::regex(R"(\n)"), false);
     // numbered_elements states = line_states(lines);
diff --git a/sks/document/reference.h b/sks/document/reference.h
index 524b857..06b68a1 100644
--- a/sks/document/reference.h
+++ b/sks/document/reference.h
@@ -11,12 +11,12 @@ using numbered_element_spec = std::tuple<std::string, std::string, std::string>;
 //using numbered_elements = std::vector<std::vector<numbered_element_spec>>;
 using numbered_elements = std::vector<numbered_element_spec>;
 
-numbered_elements html_line_states(std::vector<std::string> lines);
-numbered_elements latex_line_states(std::vector<std::string> lines);
+numbered_elements html_line_states(const std::vector<std::string>& lines);
+numbered_elements latex_line_states(const std::vector<std::string>& lines);
 
-std::pair<std::string, int> add_html_caption_numbers(std::string html_text, int& chapter_number);
-std::string add_latex_caption_numbers(std::string text);
+std::pair<std::string, int> add_html_caption_numbers(const std::string& html_text, int& chapter_number);
+std::string add_latex_caption_numbers(const std::string& text);
 
 std::string resolve_caption_references(
-    std::string target, std::vector<std::string> lines, numbered_elements states);
+    const std::string& target, const std::vector<std::string>& lines, numbered_elements states);
 
diff --git a/sks/kutil/klammer_base.cpp b/sks/kutil/klammer_base.cpp
index efed78b..4d7eacc 100644
--- a/sks/kutil/klammer_base.cpp
+++ b/sks/kutil/klammer_base.cpp
@@ -5,7 +5,7 @@
 #include "klammer_base.h"
 #include "show.h"
 
-std::string Klammer_base::get(std::string name)
+std::string Klammer_base::get(const std::string& name)
 {
     //std::cout << "GET " << name << "\n";
     std::string result = m_machine.m_state.value(name);
@@ -49,7 +49,7 @@ std::string Klammer_base::result()
         throw Target_error("Unknown target: " + target);
 }
 
-void Klammer_base::show(std::string klammer_name)
+void Klammer_base::show(const std::string& klammer_name)
 {
     std::cout << "Arguments of klammer \"" << klammer_name << "\"\n"
               << m_machine.m_state.describe() << "\n";
diff --git a/sks/kutil/klammer_base.h b/sks/kutil/klammer_base.h
index 5315059..f96ad37 100644
--- a/sks/kutil/klammer_base.h
+++ b/sks/kutil/klammer_base.h
@@ -18,14 +18,14 @@ public:
         {};
     virtual ~Klammer_base() {};
 
-    std::string get(std::string);
+    std::string get(const std::string& name);
     std::string get(const char* name);
     virtual std::string html();
     virtual std::string tex();
     virtual std::string txt();
 
     std::string result();
-    void show(std::string klammer_name);
+    void show(const std::string& klammer_name);
 
     Machine m_machine;
 };
diff --git a/sks/kutil/kutil.cpp b/sks/kutil/kutil.cpp
index 379d440..7d98e33 100644
--- a/sks/kutil/kutil.cpp
+++ b/sks/kutil/kutil.cpp
@@ -10,7 +10,7 @@
 
 #include <filesystem>
 
-std::string read_file(std::string filename)
+std::string read_file(const std::string& filename)
 {
   std::ifstream stream {};
   std::ostringstream buffer {};
@@ -36,7 +36,7 @@ std::string klammertext_dir()
   return kdir;
 }
 
-bool in_subset(std::string base, std::vector<std::string> subset)
+bool in_subset(const std::string& base, const std::vector<std::string>& subset)
 {
     return subset.empty() ||
         (std::find(subset.begin(), subset.end(), base) != subset.end());
@@ -44,7 +44,7 @@ bool in_subset(std::string base, std::vector<std::string> subset)
 
     
 
-std::vector<std::string> sks_files_of_type(std::string extension, std::vector<std::string> subset)
+std::vector<std::string> sks_files_of_type(const std::string& extension, const std::vector<std::string>& subset)
 {
     bool dbg = false;
     std::string kdir = klammertext_dir();
@@ -85,7 +85,7 @@ std::vector<std::string> sks_files_of_type(std::string extension, std::vector<st
     return result;
 }
 
-std::string find_kt_file(std::string filename)
+std::string find_kt_file(const std::string& filename)
 {
     std::string result {};
     std::vector<std::string> prefix {"", "kt/"};
@@ -117,7 +117,7 @@ std::string find_kt_file(std::string filename)
 }
 
 
-std::string caption_marker(std::string name, std::string caption, std::string delimiter)
+std::string caption_marker(const std::string& name, const std::string& caption, const std::string& delimiter)
 {
     std::string result {caption};
     if (caption.size() > 0) {
@@ -128,7 +128,7 @@ std::string caption_marker(std::string name, std::string caption, std::string de
 }
 
 /*
-std::string process(Machine& M, std::string target, fs::path source_filename,
+std::string process(Machine& M, const std::string& target, const fs::path& source_filename,
                     bool post_process, bool unescape_chars)
 {
     // Text text(source_filename, false, false);
@@ -144,7 +144,7 @@ std::string process(Machine& M, std::string target, fs::path source_filename,
     return processed;
 }
 
-std::string process(Machine& M, std::string target, std::string source_text,
+std::string process(Machine& M, const std::string& target, const std::string& source_text,
                     bool post_process, bool unescape_chars)
 {
     Text text(source_text, false, false);
@@ -157,8 +157,8 @@ std::string process(Machine& M, std::string target, std::string source_text,
     return processed;
 }
 
-std::string process(Machine& M, std::string target,
-                    std::string source_text, fs::path source_filename,
+std::string process(Machine& M, const std::string& target,
+                    const std::string& source_text, const fs::path& source_filename,
                     bool post_process, bool unescape_chars)
 {
     Text text({source_text}, {source_filename}, false, false);
diff --git a/sks/kutil/kutil.h b/sks/kutil/kutil.h
index 1babd7d..f2457a6 100644
--- a/sks/kutil/kutil.h
+++ b/sks/kutil/kutil.h
@@ -12,24 +12,24 @@ std::vector<std::string> sks_basenames { // removed "book"
 
 const std::string caption_delimiter = "__CAPTION__";
 
-std::string read_file(std::string filename);
+std::string read_file(const std::string& filename);
 
 std::string klammertext_dir();
 
-std::vector<std::string> old_sks_files_of_type(std::string extension);
-std::vector<std::string> sks_files_of_type(std::string extension, std::vector<std::string> subset={});
+std::vector<std::string> old_sks_files_of_type(const std::string& extension);
+std::vector<std::string> sks_files_of_type(const std::string& extension, const std::vector<std::string>& subset={});
 
-std::string caption_marker(std::string name, std::string caption, std::string delimiter=" – ");
+std::string caption_marker(const std::string& name, const std::string& caption, const std::string& delimiter=" – ");
 
-std::string find_kt_file(std::string filename);
+std::string find_kt_file(const std::string& filename);
 
-std::string process(Machine& M, std::string target, std::string source_text,
+std::string process(Machine& M, const std::string& target, const std::string& source_text,
                     bool post_process=false, bool unescape_chars=false);
 
-std::string process(Machine& M, std::string target, fs::path source_filename,
+std::string process(Machine& M, const std::string& target, const fs::path& source_filename,
                     bool post_process=false, bool unescape_chars=false);
 
-std::string process(Machine& M, std::string target,
-                    std::string source_text, fs::path source_filename,
+std::string process(Machine& M, const std::string& target,
+                    const std::string& source_text, const fs::path& source_filename,
                     bool post_process, bool unescape_chars);
 
diff --git a/sks/sks.k b/sks/sks.k
index c5f432b..7307f80 100644
--- a/sks/sks.k
+++ b/sks/sks.k
@@ -1,15 +1,10 @@
 # Standard Klammer Set
-@read kutil/kutil.k @
-@read target/target.k @
-@read font/font.k @
-@read section/section.k @
-@read image/image.k @
-@read code/code.k @
-@read list/list.k @
-@read link/link.k @
-@read table/table.k @
-@read date/date.k @
-@read block/block.k @
-@read color/color.k @
-@read document/document.k @
-@read book/book.k @
+@@@klammerset sks | Document production: formatting, structure, and layout for the html, tex, pdf, and txt targets
+  :name Standard Klammer Set
+  :author Andy Kopra
+  :date 2026-07-30
+  :files kutil/kutil.k target/target.k font/font.k section/section.k
+         image/image.k code/code.k list/list.k link/link.k
+         table/table.k date/date.k block/block.k color/color.k
+         document/document.k book/book.k
+@@@
diff --git a/sks/target/html_util.cpp b/sks/target/html_util.cpp
index 604e5da..fa01db8 100644
--- a/sks/target/html_util.cpp
+++ b/sks/target/html_util.cpp
@@ -132,7 +132,7 @@ std::string to_string(elements_t e)
 
 
 
-bool HTML::void_element(std::string tag) const
+bool HTML::void_element(const std::string& tag) const
 {
     if (tag == "!DOCTYPE")
         return true;
@@ -141,7 +141,7 @@ bool HTML::void_element(std::string tag) const
             (m_void_tags.begin(), m_void_tags.end(), tag) != m_void_tags.end();
 }
 
-bool HTML::empty_element(std::string tag) const
+bool HTML::empty_element(const std::string& tag) const
 {
     if (tag == preamble_tag)
         return true;
@@ -151,13 +151,13 @@ bool HTML::empty_element(std::string tag) const
 }
 
 //HTML& HTML::attr(std::string name, std::variant<int, float, std::string> value)
-HTML& HTML::attr(std::string name, attr_t value)
+HTML& HTML::attr(const std::string& name, attr_t value)
 {
     m_attrs.push_back({name, value});
     return *this;
 }
 
-HTML& HTML::attrs(std::string s)
+HTML& HTML::attrs(const std::string& s)
 {
     static const std::regex attr_rgx(R"((\w+)\s*=\s*\"(.*?)\")");
     auto attrs_begin = std::sregex_iterator(s.begin(), s.end(), attr_rgx);
@@ -177,25 +177,25 @@ HTML& HTML::attrs(std::string s)
 
 namespace html {
 
-    HTML elt(std::string tag)
+    HTML elt(const std::string& tag)
     {
         HTML h(tag);
         return h;
     }
 
-    HTML elt(std::string tag, std::string text)
+    HTML elt(const std::string& tag, const std::string& text)
     {
         HTML h(tag, trim(text));
         return h;
     }
 
-    HTML elt(std::string tag, elements_t elements)
+    HTML elt(const std::string& tag, elements_t elements)
     {
         HTML h(tag, elements);
         return h;
     }
 
-    HTML elt(std::string tag, HTML e, elements_t elts)
+    HTML elt(const std::string& tag, HTML e, elements_t elts)
     {
         elements_t elements = {e};
         elements.insert(elements.end(), elts.begin(), elts.end());
@@ -242,7 +242,7 @@ namespace html {
         return result;
     }
 
-    elements_t local_font_elements(strings_t fontnames)
+    elements_t local_font_elements(const strings_t& fontnames)
     {
         elements_t result {};
         for (auto name : fontnames) {
@@ -254,7 +254,7 @@ namespace html {
         return result;
     }
 
-    elements_t javascript(std::string output_dir, strings_t js_filenames)
+    elements_t javascript(const std::string& output_dir, const strings_t& js_filenames)
     {
         //elements_t result { jquery_elements() };
         elements_t result {};
@@ -276,10 +276,10 @@ namespace html {
         return result;
     }
 
-    HTML head(std::string title,
-              std::string css,
-              strings_t css_filenames,
-              strings_t local_fonts)
+    HTML head(const std::string& title,
+              const std::string& css,
+              const strings_t& css_filenames,
+              const strings_t& local_fonts)
     {
         elements_t elts = meta_elements();
         // msg() << "ELTS sks: " << elts << "\n";
@@ -317,8 +317,8 @@ namespace html {
     }    
 
 
-    HTML button(std::string id, std::string name,
-                std::string attrib="", std::string value="")
+    HTML button(const std::string& id, const std::string& name,
+                const std::string& attrib="", const std::string& value="")
     {
         std::vector<std::string> hidden = {"Clear", "Back"};
         HTML result = elt("span", string_replace(name, " ", "&#160;")).id(id).cls("navb");
@@ -449,7 +449,7 @@ namespace html {
         return result; 
     }
 
-    elements_t status(std::string date, std::string version, std::string copyright)
+    elements_t status(const std::string& date, const std::string& version, const std::string& copyright)
     {
         elements_t result {};
         if (!date.empty()) {
@@ -465,21 +465,21 @@ namespace html {
     }
 
     elements_t page(
-        std::string title,
+        const std::string& title,
         std::string page_title,
-        std::string output_dir,
-        std::string nav,
+        const std::string& output_dir,
+        const std::string& nav,
         int max_level,
-        std::string toc,
-        std::string text,
-        std::string date,
-        std::string version,
-        std::string copyright,
-        std::string css,
-        strings_t css_filenames,
-        strings_t js_filenames,
-        strings_t local_fonts,
-        std::string logo)
+        const std::string& toc,
+        const std::string& text,
+        const std::string& date,
+        const std::string& version,
+        const std::string& copyright,
+        const std::string& css,
+        const strings_t& css_filenames,
+        const strings_t& js_filenames,
+        const strings_t& local_fonts,
+        const std::string& logo)
     {
         if (page_title.empty())
             page_title = title;
@@ -540,7 +540,7 @@ namespace html {
     }
 
 
-    void add_title(elements_t& body, std::string title, std::string logo)
+    void add_title(elements_t& body, const std::string& title, const std::string& logo)
     {
         // No title bar at all when there is nothing to put in it (an
         // untitled document); a logo alone still gets the bar.
@@ -561,7 +561,7 @@ namespace html {
         body.push_back(navigation(max_level));
     }
 
-    void add_text(elements_t& body, std::string text, std::string toc, bool text_only)
+    void add_text(elements_t& body, const std::string& text, const std::string& toc, bool text_only)
     {
         if (text_only) {
             elements_t content {};
@@ -580,7 +580,7 @@ namespace html {
     }
 
     void add_status_bar(
-        elements_t& body, std::string date, std::string version, std::string copyright)
+        elements_t& body, const std::string& date, const std::string& version, const std::string& copyright)
     {
         elements_t status_elements = status(date, version, copyright);
         if (!empty(status_elements)) {
@@ -593,7 +593,7 @@ namespace html {
             body.push_back(elt("div", "").attr("id", "pagecache"));
     }
 
-    void add_js_links(elements_t& body, strings_t js_filenames, std::string output_dir) 
+    void add_js_links(elements_t& body, const strings_t& js_filenames, const std::string& output_dir) 
     {
         if (!js_filenames.empty()) {
             auto js_elements { javascript(output_dir, js_filenames) };
@@ -603,8 +603,8 @@ namespace html {
 
     elements_t make_page(
         elements_t body,
-        std::string page_title, std::string css,
-        strings_t css_filenames, strings_t local_fonts)
+        std::string page_title, const std::string& css,
+        const strings_t& css_filenames, const strings_t& local_fonts)
     {
         elements_t page { preamble() };
         page.push_back(
@@ -615,7 +615,7 @@ namespace html {
         return page;
     }
 
-    bool tag_is_block_element(std::string tag)
+    bool tag_is_block_element(const std::string& tag)
     {
         auto location = std::find(block_elements.begin(), block_elements.end(), tag);
         return location != block_elements.end();
@@ -635,7 +635,7 @@ namespace html {
         return result;
     }
 
-    std::string make_paragraphs(std::string html_text)
+    std::string make_paragraphs(const std::string& html_text)
     {
         (void)K::log(3);
         std::string result {};
@@ -654,7 +654,7 @@ namespace html {
         return result;
     }
 
-    std::string minimize_css(std::string src)
+    std::string minimize_css(const std::string& src)
     {
         (void)K::log(3);
         std::string result = src;
@@ -668,7 +668,7 @@ namespace html {
         return result;
     }
 
-    std::string minimize_js(std::string src)
+    std::string minimize_js(const std::string& src)
     {
         (void)K::log(3);
         return src;
diff --git a/sks/target/html_util.h b/sks/target/html_util.h
index d71b17e..34c57d0 100644
--- a/sks/target/html_util.h
+++ b/sks/target/html_util.h
@@ -32,24 +32,24 @@ public:
     operator std::string() {
         std::stringstream ss {}; ss << *this; return ss.str(); };
 
-    HTML(std::string tag) :
+    HTML(const std::string& tag) :
         m_tag(tag) {};
 
-    HTML(std::string tag, std::string text) :
+    HTML(const std::string& tag, const std::string& text) :
         m_tag(tag), m_text({text}) {};
 
-    HTML(std::string tag, elements_t elements) :
+    HTML(const std::string& tag, elements_t elements) :
         m_tag(tag), m_elements(elements) {};
 
-    HTML& attr(std::string name, attr_t value);
-    HTML& attrs(std::string s);
+    HTML& attr(const std::string& name, attr_t value);
+    HTML& attrs(const std::string& s);
 
-    HTML& cls(std::string name) { return attr("class", name); };
-    HTML& sty(std::string css) { return attr("style", css); };
-    HTML& id(std::string id) { return attr("id", id); };
+    HTML& cls(const std::string& name) { return attr("class", name); };
+    HTML& sty(const std::string& css) { return attr("style", css); };
+    HTML& id(const std::string& id) { return attr("id", id); };
 
-    bool void_element(std::string tag) const;
-    bool empty_element(std::string tag) const;
+    bool void_element(const std::string& tag) const;
+    bool empty_element(const std::string& tag) const;
     friend std::ostream& operator<<(std::ostream& os, const HTML& h);
     friend std::ostream& operator<<(std::ostream& os, const std::vector<HTML>& hv);
 
@@ -68,48 +68,48 @@ private:
 };
 
 namespace html {
-    HTML elt(std::string tag);
-    HTML elt(std::string tag, std::string text);
-    HTML elt(std::string tag, elements_t elements);
-    HTML elt(std::string tag, HTML e, elements_t elts);
+    HTML elt(const std::string& tag);
+    HTML elt(const std::string& tag, const std::string& text);
+    HTML elt(const std::string& tag, elements_t elements);
+    HTML elt(const std::string& tag, HTML e, elements_t elts);
 
     //HTML preamble();
     //HTML head(strings_t css_filenames, strings_t js_filenames);
 
     elements_t page(
-        std::string title,
+        const std::string& title,
         std::string page_title,
-        std::string output_dir,
-        std::string nav,
+        const std::string& output_dir,
+        const std::string& nav,
         int max_level,
-        std::string toc,
-        std::string text,
-        std::string date,
-        std::string version,
-        std::string copyright,
-        std::string css,
+        const std::string& toc,
+        const std::string& text,
+        const std::string& date,
+        const std::string& version,
+        const std::string& copyright,
+        const std::string& css,
         strings_t css_filenames = {},
         strings_t js_filenames = {},
         strings_t local_fonts = {},
         std::string logo = {});
 
-    void add_title(elements_t& body, std::string title, std::string logo="");
-    void add_title(elements_t& body, std::string title, std::string logo);
+    void add_title(elements_t& body, const std::string& title, const std::string& logo="");
+    void add_title(elements_t& body, const std::string& title, const std::string& logo);
     void add_nav(elements_t& body, int max_level);
-    void add_text(elements_t& body, std::string text, std::string toc_text, bool text_only);
+    void add_text(elements_t& body, const std::string& text, const std::string& toc_text, bool text_only);
     void add_bottom_spacer(elements_t& body);
-    void add_status_bar(elements_t& body, std::string date, std::string version, std::string copyright);
+    void add_status_bar(elements_t& body, const std::string& date, const std::string& version, const std::string& copyright);
     void add_page_cache(elements_t& body);
-    void add_js_links(elements_t& body, std::vector<std::string> js_filenames, std::string output_dir);
+    void add_js_links(elements_t& body, const std::vector<std::string>& js_filenames, const std::string& output_dir);
     elements_t make_page(
         elements_t body,
-        std::string page_title, std::string css,
-        std::vector<std::string> css_filenames,
-        std::vector<std::string> local_fonts);
+        std::string page_title, const std::string& css,
+        const std::vector<std::string>& css_filenames,
+        const std::vector<std::string>& local_fonts);
 
-    bool tag_is_block_element(std::string tag);
-    std::string make_paragraphs(std::string html_text);
-    std::string minimize_css(std::string src);
-    std::string minimize_js(std::string src);
+    bool tag_is_block_element(const std::string& tag);
+    std::string make_paragraphs(const std::string& html_text);
+    std::string minimize_css(const std::string& src);
+    std::string minimize_js(const std::string& src);
 
 }
diff --git a/sks/target/latex_util.cpp b/sks/target/latex_util.cpp
index 42a0a54..94e2c05 100644
--- a/sks/target/latex_util.cpp
+++ b/sks/target/latex_util.cpp
@@ -33,7 +33,7 @@ namespace latex {
 
 
     std::string title_line(
-        std::string text, std::string font="1.3", std::string vskip="4pt",
+        const std::string& text, const std::string& font="1.3", const std::string& vskip="4pt",
         bool vskip_if_missing=false)
     {
         std::stringstream ss {};
@@ -48,8 +48,8 @@ namespace latex {
     }
 
     std::string default_cover(
-        std::string title, std::string subtitle,
-        std::string author, std::string date, std::string version)
+        const std::string& title, const std::string& subtitle,
+        const std::string& author, const std::string& date, const std::string& version)
     {
         std::string test = trim(title + subtitle + author + date + version);
         std::stringstream ss {};
@@ -65,8 +65,8 @@ namespace latex {
     }
 
     std::string nonbook_title(
-        std::string title, std::string subtitle,
-        std::string author, std::string date, std::string version)
+        const std::string& title, const std::string& subtitle,
+        const std::string& author, const std::string& date, const std::string& version)
     {
         std::string test = trim(title + subtitle + author + date + version);
         std::stringstream ss {};
@@ -86,7 +86,7 @@ namespace latex {
         return ss.str();
     }
 
-    std::string pagenumber(int n, std::string style="arabic")
+    std::string pagenumber(int n, const std::string& style="arabic")
     {
         (void)K::log(3);
         std::stringstream ss {};
@@ -94,7 +94,7 @@ namespace latex {
         return ss.str();
     }
 
-    std::string book_verso_page(std::string copyright)
+    std::string book_verso_page(const std::string& copyright)
     {
         (void)K::log(3);
         std::stringstream ss {};
@@ -111,7 +111,7 @@ namespace latex {
         return ss.str();
     }
     
-    std::string font_command(std::string command, const Resolved_font& font, float scale)
+    std::string font_command(const std::string& command, const Resolved_font& font, float scale)
     {
         std::stringstream ss {};
         if (font.family_name.empty())
@@ -150,23 +150,23 @@ namespace latex {
         return ss.str();
     }
 
-    std::string page(std::string structure,
-                     std::string title,
-                     std::string subtitle,
-                     std::string authors,
-                     std::string date,
-                     std::string version,
-                     std::string copyright,
-                     std::string bottom,
-                     std::string prolog,
-                     std::string paper_size,
+    std::string page(const std::string& structure,
+                     const std::string& title,
+                     const std::string& subtitle,
+                     const std::string& authors,
+                     const std::string& date,
+                     const std::string& version,
+                     const std::string& copyright,
+                     const std::string& bottom,
+                     const std::string& prolog,
+                     const std::string& paper_size,
                      bool two_column,
                      float leading,
                      int pointsize,
                      bool ragged_right,
-                     std::string cover,
+                     const std::string& cover,
                      bool landscape,
-                     std::string body,
+                     const std::string& body,
                      Resolved_font serif_font,
                      Resolved_font sans_font,
                      Resolved_font mono_font,
diff --git a/sks/target/latex_util.h b/sks/target/latex_util.h
index 358769c..1380ece 100644
--- a/sks/target/latex_util.h
+++ b/sks/target/latex_util.h
@@ -6,23 +6,23 @@
 
 namespace latex {
 
-std::string page(std::string structure,
-                 std::string title,
-                 std::string subtitle,
-                 std::string authors,
-                 std::string date,
-                 std::string version,
-                 std::string copyright,
-                 std::string bottom,
-                 std::string prolog,
-                 std::string paper_size,
+std::string page(const std::string& structure,
+                 const std::string& title,
+                 const std::string& subtitle,
+                 const std::string& authors,
+                 const std::string& date,
+                 const std::string& version,
+                 const std::string& copyright,
+                 const std::string& bottom,
+                 const std::string& prolog,
+                 const std::string& paper_size,
                  bool two_column,
                  float leading,
                  int pointsize,
                  bool ragged_right,
-                 std::string cover,
+                 const std::string& cover,
                  bool landscape,
-                 std::string body,
+                 const std::string& body,
                  Resolved_font serif_font = {},
                  Resolved_font sans_font = {},
                  Resolved_font mono_font = {},
diff --git a/sks/target/target.k b/sks/target/target.k
index f771ebf..b923701 100644
--- a/sks/target/target.k
+++ b/sks/target/target.k
@@ -3,7 +3,7 @@ The targets in the SKS use the LaTeX convention for converting ASCII
 characters into standard typographical characters.  This is done
 by LaTeX by default; other targets must use the transforms parameter
 of Parameter_set, as defined for the m_parameters variable of the
-Target_set class.  (See file target_set.cpp.)
+Target_registry class.  (See file target_registry.cpp.)
 
 The LaTeX transformations supported by the SKS are:
 
diff --git a/tst/Makefile b/tst/Makefile
index 2e12c6c..1063458 100644
--- a/tst/Makefile
+++ b/tst/Makefile
@@ -1,6 +1,6 @@
 # Klammertext distribution test suite (subset).
 #
-# Runs the seven shell regression suites:
+# Runs the eight shell regression suites:
 #   cond_test.sh     — @cond argument delimitation
 #   deftype_test.sh  — the four klammer definition modes + redefinition table
 #   escape_test.sh   — target character escaping and quoted specials
@@ -8,6 +8,7 @@
 #   alone_test.sh    — an optional argument's three values (default, the
 #                      argument type's :alone value, a written value)
 #   modulepath_test.sh — @eval finds modules beside the file that names them
+#   klammerset_test.sh — the @@@klammerset system command and its search path
 #   editor_test.sh   — editor support (doc/edit): indentation and table
 #                      alignment; needs python3, uses Emacs when installed
 #
@@ -21,4 +22,5 @@ test:
 	./filename_test.sh
 	./alone_test.sh
 	./modulepath_test.sh
+	./klammerset_test.sh
 	./editor_test.sh
diff --git a/tst/deftype_test.sh b/tst/deftype_test.sh
index a16dd22..575d802 100755
--- a/tst/deftype_test.sh
+++ b/tst/deftype_test.sh
@@ -17,7 +17,7 @@
 # combinations. This test pins down every entry of that table plus the basic
 # behavior of each mode, none of which tst/klammer_test.cpp currently covers.
 #
-# {replace,warn,message} semantics (mac/klammer_set.cpp):
+# {replace,warn,message} semantics (mac/klammer_registry.cpp):
 #   !replace && message  -> Definition_error (nonzero exit)
 #   !replace && empty    -> silently keep the existing definition
 #   replace  && warn     -> emit a warning, then replace
diff --git a/tst/klammerset/bad_file.k b/tst/klammerset/bad_file.k
new file mode 100644
index 0000000..1df398e
--- /dev/null
+++ b/tst/klammerset/bad_file.k
@@ -0,0 +1 @@
+@@@klammerset broken | Lists a file that does not exist :files missing.k @@@
diff --git a/tst/klammerset/base.k b/tst/klammerset/base.k
new file mode 100644
index 0000000..1b68c14
--- /dev/null
+++ b/tst/klammerset/base.k
@@ -0,0 +1 @@
+@@@target fix | Fixture target @@@
diff --git a/tst/klammerset/decl.k b/tst/klammerset/decl.k
new file mode 100644
index 0000000..57f5b51
--- /dev/null
+++ b/tst/klammerset/decl.k
@@ -0,0 +1,11 @@
+# Engine-tier fixture: a klammerset with metadata, a dependency, an ordered
+# file list (klammers.k uses the target defined in base.k), and a trailing
+# definition that must load after the files (program order).
+@@@klammerset kit | Engine-test klammerset
+  :name Klammerset Integration Test
+  :author Klammertext tests
+  :date 2026-07-30
+  :requires util.k
+  :files base.k / klammers.k
+@@@
+@@after : AFTER @@
diff --git a/tst/klammerset/decl2.k b/tst/klammerset/decl2.k
new file mode 100644
index 0000000..41c9e42
--- /dev/null
+++ b/tst/klammerset/decl2.k
@@ -0,0 +1 @@
+@@@klammerset kit | Duplicate declaration of kit :files dup_only.k @@@
diff --git a/tst/klammerset/dup_only.k b/tst/klammerset/dup_only.k
new file mode 100644
index 0000000..1d6bcdc
--- /dev/null
+++ b/tst/klammerset/dup_only.k
@@ -0,0 +1 @@
+@@only_dup : DUP @@
diff --git a/tst/klammerset/klammers.k b/tst/klammerset/klammers.k
new file mode 100644
index 0000000..3e7992c
--- /dev/null
+++ b/tst/klammerset/klammers.k
@@ -0,0 +1 @@
+@@greet.fix name : Hello *name* @@
diff --git a/tst/klammerset/space name.k b/tst/klammerset/space name.k
new file mode 100644
index 0000000..b006dbf
--- /dev/null
+++ b/tst/klammerset/space name.k	
@@ -0,0 +1 @@
+@@spacey.fix : SPACEY @@
diff --git a/tst/klammerset/spacey.k b/tst/klammerset/spacey.k
new file mode 100644
index 0000000..4e63bf2
--- /dev/null
+++ b/tst/klammerset/spacey.k
@@ -0,0 +1 @@
+@@@klammerset sp | Spacey filename in the list :files base.k / space name.k @@@
diff --git a/tst/klammerset/util.k b/tst/klammerset/util.k
new file mode 100644
index 0000000..53b87fc
--- /dev/null
+++ b/tst/klammerset/util.k
@@ -0,0 +1,2 @@
+@@@klammerset util | Utility klammers for engine tests :date 2026-07-30 @@@
+@@dash : -- @@
diff --git a/tst/klammerset/wrapper.k b/tst/klammerset/wrapper.k
new file mode 100644
index 0000000..cbfb1e4
--- /dev/null
+++ b/tst/klammerset/wrapper.k
@@ -0,0 +1 @@
+@@@klammerset wrap | Wrapper requiring kit twice :requires decl.k / decl2.k @@@
diff --git a/tst/klammerset_test.sh b/tst/klammerset_test.sh
new file mode 100755
index 0000000..c17ff45
--- /dev/null
+++ b/tst/klammerset_test.sh
@@ -0,0 +1,284 @@
+#!/bin/bash
+#
+# klammerset_test.sh — Regression tests for the @@@klammerset system command.
+#
+# @@@klammerset declares a Klammerset: a named, logically related group of
+# klammer definitions.  The declaration is operative — processing it reads
+# the :requires files and then the :files, in list order, at the point of the
+# declaration; relative names resolve against the declaring file's directory,
+# never the cwd.  A repeated declaration of an already-registered symbol is
+# skipped (loaded once), which is what makes :requires idempotent.  The
+# klammers themselves live in the Machine's flat Klammer_registry; the
+# Klammerset holds metadata and the file list only.
+#
+# Engine tier: no SKS.  Fixtures live in tst/klammerset/ and define their own
+# target ("fix") inline.
+#
+# Usage: ./klammerset_test.sh
+# Exit code: 0 if all tests pass, 1 otherwise.
+
+PASS=0
+FAIL=0
+KTEXT=ktext
+K=${KLAMMERTEXT_HOME:?KLAMMERTEXT_HOME must be set}
+FIX=$K/tst/klammerset
+
+red=$'\033[31m'
+green=$'\033[32m'
+bold=$'\033[1m'
+reset=$'\033[0m'
+
+# strip leading/trailing blank lines and surrounding whitespace
+trim() { awk '{ sub(/[ \t\r]+$/, "") } { line[NR]=$0 } END { f=1; while (f<=NR && line[f]=="") f++; l=NR; while (l>=1 && line[l]=="") l--; for (i=f;i<=l;i++) print line[i] }'; }
+
+# check_eq TEST_NAME EXPECTED KTEXT_ARGS...
+#   Runs ktext, expects exit status 0, and compares trimmed stdout to EXPECTED.
+check_eq() {
+    local test_name="$1"
+    local expected="$2"
+    shift 2
+
+    local output status
+    output=$("$KTEXT" "$@" 2>/tmp/klammerset_test_err.$$)
+    status=$?
+    output=$(printf '%s' "$output" | trim)
+
+    if [ $status -ne 0 ]; then
+        echo "${red}FAIL${reset} $test_name — ktext exited $status"
+        echo "       stderr: $(head -3 /tmp/klammerset_test_err.$$)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    if [ "$output" = "$expected" ]; then
+        echo "${green}PASS${reset} $test_name"
+        PASS=$((PASS + 1))
+    else
+        echo "${red}FAIL${reset} $test_name"
+        echo "       expected: [$expected]"
+        echo "       got:      [$output]"
+        FAIL=$((FAIL + 1))
+    fi
+}
+
+# check_contains TEST_NAME SUBSTRING KTEXT_ARGS...
+#   Runs ktext, expects exit status 0, and checks that the combined output
+#   contains SUBSTRING.
+check_contains() {
+    local test_name="$1"
+    local needle="$2"
+    shift 2
+
+    local output status
+    output=$("$KTEXT" "$@" 2>&1)
+    status=$?
+
+    if [ $status -ne 0 ]; then
+        echo "${red}FAIL${reset} $test_name — ktext exited $status"
+        echo "       output: $(echo "$output" | head -3)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    if printf '%s' "$output" | grep -qF "$needle"; then
+        echo "${green}PASS${reset} $test_name"
+        PASS=$((PASS + 1))
+    else
+        echo "${red}FAIL${reset} $test_name"
+        echo "       expected output to contain: [$needle]"
+        echo "       got: $(echo "$output" | head -5)"
+        FAIL=$((FAIL + 1))
+    fi
+}
+
+# check_fails TEST_NAME SUBSTRING KTEXT_ARGS...
+#   Runs ktext, expects a NONZERO exit status, and checks that the combined
+#   output contains SUBSTRING.
+check_fails() {
+    local test_name="$1"
+    local needle="$2"
+    shift 2
+
+    local output status
+    output=$("$KTEXT" "$@" 2>&1)
+    status=$?
+
+    if [ $status -eq 0 ]; then
+        echo "${red}FAIL${reset} $test_name — expected an error, ktext exited 0"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    if printf '%s' "$output" | grep -qF "$needle"; then
+        echo "${green}PASS${reset} $test_name"
+        PASS=$((PASS + 1))
+    else
+        echo "${red}FAIL${reset} $test_name"
+        echo "       expected error output to contain: [$needle]"
+        echo "       got: $(echo "$output" | head -5)"
+        FAIL=$((FAIL + 1))
+    fi
+}
+
+echo "${bold}@@@klammerset tests${reset}"
+echo "======================="
+echo
+
+# --- Loading ---------------------------------------------------------------
+
+# 1. :files load in list order: klammers.k defines @greet for the target
+#    that base.k declares, so base.k must have been read first.
+check_eq "1. :files load in order (target before klammer)" \
+    "Hello World" \
+    -k "$FIX/decl.k" -s '@greet World @' -t fix
+
+# 2. :requires loads the dependency before the set's own files.
+check_eq "2. :requires loads the dependency" \
+    "--" \
+    -k "$FIX/decl.k" -s '@dash@' -t fix
+
+# 3. Program order: a definition AFTER the declaration in the declaring file
+#    is available (there is no :text argument; the declaring file's own
+#    content plays that role).
+check_eq "3. trailing definition in the declaring file" \
+    "AFTER" \
+    -k "$FIX/decl.k" -s '@after@' -t fix
+
+# 4. Relative :files names resolve against the DECLARING file's directory,
+#    not the cwd (run from an unrelated directory).
+output=$( (cd /tmp && "$KTEXT" -k "$FIX/decl.k" -s '@greet Elsewhere @' -t fix) 2>/dev/null | trim )
+if [ "$output" = "Hello Elsewhere" ]; then
+    echo "${green}PASS${reset} 4. :files resolve against the declaring file's directory"
+    PASS=$((PASS + 1))
+else
+    echo "${red}FAIL${reset} 4. :files resolve against the declaring file's directory"
+    echo "       expected: [Hello Elsewhere]"
+    echo "       got:      [$output]"
+    FAIL=$((FAIL + 1))
+fi
+
+# 5. A filename with a space in the :files list (standalone "/" separator).
+check_eq "5. spacey filename in :files" \
+    "SPACEY" \
+    -k "$FIX/spacey.k" -s '@spacey@' -t fix
+
+# --- The already-loaded guard ------------------------------------------------
+
+# 6. A second declaration of an already-registered symbol is skipped, not an
+#    error: wrapper.k requires decl.k (registers "kit") and then decl2.k
+#    (re-declares "kit"); the wrapper still loads and kit's klammers work.
+check_eq "6. duplicate declaration is skipped, not an error" \
+    "Hello Again" \
+    -k "$FIX/wrapper.k" -s '@greet Again @' -t fix
+
+# 7. ...and the skipped declaration's files are NOT loaded.
+check_fails "7. skipped declaration loads none of its files" \
+    "only_dup" \
+    -k "$FIX/wrapper.k" -s '@only_dup@' -t fix
+
+# --- Introspection -----------------------------------------------------------
+
+# 8. -m lists the registered klammersets.
+check_contains "8. -m shows the klammerset symbol" \
+    "kit" \
+    -k "$FIX/decl.k" -s 'x' -t fix -m
+
+check_contains "9. -m shows the required klammerset too" \
+    "Utility klammers for engine tests" \
+    -k "$FIX/decl.k" -s 'x' -t fix -m
+
+# --- Errors --------------------------------------------------------------------
+
+# 10. A listed file that does not exist is a clean klammerset error.
+check_fails "10. missing file in :files" \
+    "missing.k" \
+    -k "$FIX/bad_file.k" -s 'x' -t fix
+
+# 11. A symbol must be an identifier (starts with a letter; letters, digits,
+#     underscores).
+check_fails "11. invalid symbol rejected" \
+    "not valid" \
+    -k none -s '@@@klammerset 9bad | Bad symbol @@@' -d
+
+# --- The search path (symbol -> <dir>/<symbol>/<symbol>.k) -------------------
+
+# Runtime fixtures: a document directory holding a local klammerset, and a
+# separate directory serving as a KLAMMERTEXT_KLAMMERSETS stage.
+DOCDIR=$(mktemp -d /tmp/klammerset_doc.XXXXXX)
+ENVDIR=$(mktemp -d /tmp/klammerset_env.XXXXXX)
+trap 'rm -rf "$DOCDIR" "$ENVDIR" /tmp/klammerset_test_err.$$' EXIT
+
+mkdir -p "$DOCDIR/locset" "$ENVDIR/envset" "$ENVDIR/locset"
+printf '@@@klammerset locset | Document-local set @@@\n@@@target fixL | Fixture @@@\n@@local_k.fixL : LOCAL @@\n' \
+    > "$DOCDIR/locset/locset.k"
+printf '@local_k@\n' > "$DOCDIR/doc.kt"
+printf '@@@klammerset envset | Installed set @@@\n@@@target fixE | Fixture @@@\n@@env_k.fixE : ENV @@\n' \
+    > "$ENVDIR/envset/envset.k"
+printf '@@@klammerset locset | Shadow candidate @@@\n@@@target fixL | Fixture @@@\n@@local_k.fixL : ENV-SHADOWED @@\n' \
+    > "$ENVDIR/locset/locset.k"
+
+# 12. Stage 1 for a file input: the document's directory.
+check_eq "12. symbol resolves in the document's directory" \
+    "LOCAL" \
+    "$DOCDIR/doc.kt" -k locset -t fixL -d
+
+# 13. Stage 1 for string input: the cwd stands in for the document.
+output=$( (cd "$DOCDIR" && "$KTEXT" -s '@local_k@' -k locset -t fixL) 2>/dev/null | trim )
+if [ "$output" = "LOCAL" ]; then
+    echo "${green}PASS${reset} 13. cwd stands in for the document (string input)"
+    PASS=$((PASS + 1))
+else
+    echo "${red}FAIL${reset} 13. cwd stands in for the document (string input)"
+    echo "       expected: [LOCAL]  got: [$output]"
+    FAIL=$((FAIL + 1))
+fi
+
+# 14. Stage 2: the KLAMMERTEXT_KLAMMERSETS directories.
+output=$(KLAMMERTEXT_KLAMMERSETS=$ENVDIR "$KTEXT" -s '@env_k@' -k envset -t fixE 2>/dev/null | trim)
+if [ "$output" = "ENV" ]; then
+    echo "${green}PASS${reset} 14. symbol resolves in KLAMMERTEXT_KLAMMERSETS"
+    PASS=$((PASS + 1))
+else
+    echo "${red}FAIL${reset} 14. symbol resolves in KLAMMERTEXT_KLAMMERSETS"
+    echo "       expected: [ENV]  got: [$output]"
+    FAIL=$((FAIL + 1))
+fi
+
+# 15. Shadowing: the document-local set wins over the installed one.
+output=$(KLAMMERTEXT_KLAMMERSETS=$ENVDIR "$KTEXT" "$DOCDIR/doc.kt" -k locset -t fixL -d 2>/dev/null | trim)
+if [ "$output" = "LOCAL" ]; then
+    echo "${green}PASS${reset} 15. document-local set shadows the installed one"
+    PASS=$((PASS + 1))
+else
+    echo "${red}FAIL${reset} 15. document-local set shadows the installed one"
+    echo "       expected: [LOCAL]  got: [$output]"
+    FAIL=$((FAIL + 1))
+fi
+
+# 16. :requires by symbol, resolved with the declaring directory as the
+#     local stage (the required set sits inside the declaring set's dir).
+mkdir -p "$DOCDIR/kit2/locset"
+cp "$DOCDIR/locset/locset.k" "$DOCDIR/kit2/locset/locset.k"
+printf '@@@klammerset kit2 | Requires by symbol :requires locset @@@\n' > "$DOCDIR/kit2/kit2.k"
+check_eq "16. :requires accepts a symbol (declaring-dir stage)" \
+    "LOCAL" \
+    -k "$DOCDIR/kit2/kit2.k" -s '@local_k@' -t fixL
+
+# 17. Stage 3: $KLAMMERTEXT_HOME — the kdesc listing enumerates sks
+#     (sks/sks.k already satisfies the <symbol>/<symbol>.k convention).
+output=$(kdesc --klammerset 2>/dev/null)
+if printf '%s' "$output" | grep -q 'sks/sks\.k'; then
+    echo "${green}PASS${reset} 17. kdesc --klammerset lists sks from KLAMMERTEXT_HOME"
+    PASS=$((PASS + 1))
+else
+    echo "${red}FAIL${reset} 17. kdesc --klammerset lists sks from KLAMMERTEXT_HOME"
+    echo "       got: $(echo "$output" | head -3)"
+    FAIL=$((FAIL + 1))
+fi
+
+# 18. An unknown symbol is a clean error naming the search directories.
+check_fails "18. unknown symbol names the search path" \
+    "was not found" \
+    -s 'x' -k nosuchset -d
+
+echo
+echo "======================="
+echo "Results: ${green}$PASS passed${reset}, $([ $FAIL -gt 0 ] && echo "${red}$FAIL failed${reset}" || echo "0 failed")"
+[ $FAIL -eq 0 ]