Regex Tester & Validator

A PCRE recursive regex that matches lines containing balanced, nested double-angle-bracket structures such as <<hello>> or <<a<<b>>c>>. It uses an atomic group with recursion via (?1) to support arbitrary nesting depth, while [^<>\n]+ consumes inner content without crossing line boundaries. Useful for validating or extracting nested template expressions, interpolation syntax, or guillemet-delimited blocks.