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)
