Regex Tester & Validator

Despite the lookbehind-like syntax, this is really a character class matching one or more of: ( ? < = . , ) digits, and every ASCII char from '[' to '|' — a range that includes lowercase a-z, backslash, ], ^, _ and {. It looks like a broken attempt at a lookbehind such as (?<=[-|.,])\d+ meant to capture digits after punctuation. The m flag has no effect since the pattern contains no anchors.