Regexp model

flexr compiles regular languages into an automaton. Literals, concatenation, alternation, greedy *, +, ?, bounded repetition, character classes, and supported Unicode properties are the useful core.

Construct	Status	Alternative
Literal, concatenation, alternation	Supported	—
*, +, ?	Supported	Greedy matching
{n,m}	Supported	Keep bounds explicit
Lookahead / lookbehind	Unsupported	followed_by: or a state/action
Backreferences	Unsupported	Split the rule or validate in an action
Open repetition {n,}	Unsupported	Use a separate rule/action
Capturing groups	Accepted with a diagnostic	Use (?:...) for intent

Run flexr check before relying on a construct. The regexp reference records the implementation-level boundaries.