Tartrazine

Shared empty result for rule misses (allocation cut, see patch 5). Never mutated: the only consumer iterates it into a deque.

Elements whose state attribute names a state of the same lexer.

The custom lexer for a lowercased file base name (an exact <filename> entry or a glob), or nil.

Whether lexer_by_name resolves name (lowercased), given the custom lexer names in custom: a custom or bundled name, or a+b (a delegating lexer, split at the first +) whose halves both resolve.

Parse one grammar file's XML. Returns the lowercased names it registers under (<name> first, then each <alias>), its lowercased <filename> globs, its template, warnings, and the lowercased <using lexer> names that are neither bundled nor its own (the caller checks them against the other custom grammars). Warnings cover what only fails once tokenization reaches it, so the block then falls back to plain: a <push>, <include> or <combined> naming a state the grammar does not define (three bundled grammars have one, so these warn rather than reject), a cycle of <include>s, a pattern-less rule that emits a <token>, and a negative <pop depth>. A <filename> glob File.match? would refuse is dropped with a warning. Raises with a readable message on malformed XML, a missing <name> or root state, an unknown action, or a regex PCRE2 refuses to compile.

Replace every previously registered custom lexer with entries (names, filename globs, template). Earlier entries win a name both claim; the caller orders and reports those.