# Regular expressions The 4 definitions of the regular expressions library, each with its Epsil spelling, its MathJSON name, its signature and its full description. Each definition is listed under its Epsil spelling (the MathJSON name when it has none), with its signature in the engine's type syntax. The [Standard Library](/library/) page is the one-page index of every category. ## Definitions ### isMatch MathJSON `IsMatch` · `(subject: string, pattern: regexp) -> boolean` Whether a string contains a match for a regular expression. ### regExp MathJSON `RegExp` · `(pattern: string, flags: string?) -> regexp` A compiled regular expression, using the host JavaScript dialect. The pattern is written most readably as a raw string literal: `RegExp(#"[0-9]+"#)`. ### stringMatch MathJSON `StringMatch` · `(subject: string, pattern: regexp) -> nothing | record` The first match of a regular expression in a string, as a record. The record holds `match`, `range`, `groups` and `names`; the result is `Nothing` when there is no match. ### stringMatchAll MathJSON `StringMatchAll` · `(subject: string, pattern: regexp) -> list` Every non-overlapping match of a regular expression in a string, as a list of records. Each record has the same shape as `StringMatch`.