pub fn iter_directives(s: &str) -> impl Iterator<Item = (&str, Directive<'_>)>Expand description
Iterate every ${...} directive in s, yielding the full token text
(including ${ and }) and its Directive classification. $${ is an
escape and yields nothing; an unterminated ${ ends iteration. This is
the shared tokenizer used by expand.rs validation so it scans and
classifies tokens exactly as rewrite does during substitution.