Function: highlight-regexp

Set face of each match of REGEXP to FACE.
Interactively, prompt for REGEXP then FACE, using a buffer-local
history list for REGEXP and a global history list for FACE.

If Font Lock mode is enabled in the buffer, it is used to
highlight REGEXP. If Font Lock mode is disabled, overlays are
used for highlighting; in this case, the highlighting will not be
updated as you type. (fn REGEXP &optional FACE)