* >$S ( a.str -- $: a$ )

Push the external Forth string a.str onto the string stack,
without copying the string value into the string buffer. It
is an unchecked error if the Forth string a.str is not stored
as an external measured string.
WARNING: If the string value of a.str is actually in the

string buffer and not external, the push operation may
generate a garbage collection that invalidates its MSA.

FORTH/DEF dstrings ordinary primitive