An optional argument has three values: the default (the name is absent), the argument type's :alone value (the name is written alone), and a written value. :alone is declared by the argument type only, never by a klammer's parameter declaration -- a default is what one klammer means by silence, but a bare option name must read the same way in every klammer. The bool type declares :alone true, which is the whole of the convention that a bare boolean option means true; there is no boolean special case in the engine. A type whose pattern matches running text cannot declare :alone, since an option's value runs to the next bar or option name and would swallow the following text. kdesc and `ktext -m` now show [default: X] and [alone: Y] per argument type. In the Standard Klammer Set: @code :number becomes a bool (it was an untyped string tested only for truthiness, so a bare :number was a no-op); decimal_mark declares :alone comma; table_hline and table_vline declare :alone all. The 35 bools that default false gained the bare form for free. Tests: tst/alone_test.sh (21 cases) joins the shipped suite. (from dev 6024f49c2859)
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