* lisp/emacs-lisp/rx.el (rx--translate-not): * test/lisp/emacs-lisp/rx-tests.el (rx-not, rx-def-in-not): * doc/lispref/searching.texi (Rx Constructs, Extending Rx): Allow user-defined rx constructs to be expanded inside (not ...) forms, for better composability (bug#37849).