34.3.3.2 Functions and macros using rx regexps

Macro: rx rx-expr…

Translate the rx-exprs to a string regexp, as if they were the body of a (seq …) form. The rx macro expands to a string constant, or, if literal or regexp forms are used, a Lisp expression that evaluates to a string.

Function: rx-to-string rx-expr &optional no-group

Translate rx-expr to a string regexp which is returned. If no-group is absent or nil, bracket the result in a non-capturing group, ‘\(?:…\)’, if necessary to ensure that a postfix operator appended to it will apply to the whole expression.

Arguments to literal and regexp forms in rx-expr must be string literals.

The pcase macro can use rx expressions as patterns directly; see rx in pcase.

For mechanisms to add user-defined extensions to the rx notation, see Extending Rx.