Regex Tester & Validator

Matches a zero-width position immediately before a <GTOL-IDENTIFIER> tag (literal '<GTOL-' plus uppercase letters and '>'), but only when that tag is NOT the first non-whitespace content on the line. The variable-length negative lookbehind (?<!^\s*) rejects positions preceded only by start-of-line and whitespace, while the positive lookahead asserts the tag follows. With gm flags, ^ anchors to each line. Useful for finding GTOL tags embedded mid-line while ignoring standalone line-leading tags; requires .NET for variable-length lookbehind.