Regex Tester & Validator

Matches the start of each line (multiline flag) containing an optional opening delimiter (`[`, `(`, or a literal `|`), followed by a mandatory empty parenthesis pair `()`, an optional `[]` pair, and a closing character (`]`, `|`, or `)`). Typical matches include `())`, `()]`, `[()]`, `(())`, and `|()|`. Likely intended to detect empty placeholder or bracket groups at line starts, though the character classes make it more permissive than a strict matcher.