reftex-index
reftex-index is an interactive autoloaded compiled Lisp function in `reftex-index.el
'.
(reftex-index &optional CHAR KEY TAG SEL NO-INSERT)
Query for an index macro and insert it along with its arguments.
The index macros available are those defined in `reftex-index-macro' or
by a call to `reftex-add-index-macros', typically from an AUCTeX style file.
RefteX provides completion for the index tag and the index key, and
will prompt for other arguments.