# Regular expressions — Atoms

> Atoms are the most basic units of a regular expression. Each atom _consumes_ one or more characters in the string, and either fails the match or allows the pattern to continue matching with the next atom. Backreference: \1, \2 : Matches a previously matched subpattern captured with a capturing group

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- Updated: `2026-08-16T09:32:14.499183+00:00`
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## Knowledge

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Atoms are the most basic units of a regular expression. Each atom _consumes_ one or more characters in the string, and either fails the match or allows the pattern to continue matching with the next atom.

Backreference: \1, \2 : Matches a previously matched subpattern captured with a capturing group. Capturing group: (...) : Matches a subpattern and remembers information about the match. [Character class: [...], [^...]](/en-US/docs/Web/JavaScript/Reference/Regular_expressions/Character_class) : Matches any character in or not in a set of characters. When the v flag is enabled, it can also be used to match finite-length strings. Character class escape: \d, \D, \w, \W, \s, \S : Matches any character in or not in a predefined set of characters. Character escape: \n, \u : Matches a character that may not be able to be conveniently represented in its literal form. Literal character: a, b : Matches a specific character. Modifier: (?ims-ims:...) : Overrides flag settings in a specific part of a regular expression. Named backreference: \k : Matches a previously matched subpattern captured with a named capturing group. Named capturing group: (?...) : Matches a subpattern and remembers information about the match. The group can later be identified by a custom name instead of by its index in the pattern. Non-capturing group: (?:...) : Matches a subpattern without remembering information about the match. Unicode character class escape: \p, \P : Matches a set of characters specified by a Unicode property. When the v flag is enabled, it can also be used to match finite-length strings. Wildcard: . : Matches any character except line terminators, unless the s flag is set.

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