Regex explainer

Get a plain-English breakdown of a pattern, and a safety check for ReDoS: patterns that can freeze a program on crafted input.

The timing test feeds the pattern long, almost-matching strings in a separate thread and stops it after 1.5 seconds, so a bad pattern can't freeze this page. The explanation covers common syntax and may simplify unusual patterns. Passing the test does not prove a pattern is safe for every input.