Regex Tester & Validator

Matches content between 'START' and 'Closing' markers, capturing everything lazily including newlines. The lookbehind (?<=START) requires 'START' to immediately precede the match without consuming it, while the lookahead (?=Closing) stops just before 'Closing'. The (?s) inline flag makes the dot match newline characters, enabling multiline block extraction. With the global flag, it extracts all such delimited blocks in a document, useful for parsing logs, templates, or tagged sections.