reftex-vars.el
("\\\\label{\\(?1:[^}]*\\)}" "\\[[^]]*\\ Documentation: List of regexps matching \label definitions. The default value matches usual \label{...} definitions and keyval style [..., label = {...}, ...] label definitions. It is assumed that the regexp group 1 matches the label text, so you have to define it using \(?1:...\) when adding new regexps. When changed from Lisp, make sure to call `reftex-compile-variables' afterwards to make the change effective. You can customize this variable. This variable was introduced, or its default value was changed, in version 24.4 of Emacs.