Function: highlight-changes-mode

Toggle highlighting changes in this buffer (Highlight Changes mode).
With a prefix argument ARG, enable Highlight Changes mode if ARG
is positive, and disable it otherwise. If called from Lisp,
enable the mode if ARG is omitted or nil.

When Highlight Changes is enabled, changes are marked with a text
property. Normally they are displayed in a distinctive face, but
command M-x highlight-changes-visible-mode can be used to toggles
this on and off.

Other functions for buffers in this mode include:
M-x highlight-changes-next-change - move point to beginning of next change
M-x highlight-changes-previous-change - move to beginning of previous change
M-x highlight-changes-remove-highlight - remove the change face from the region
M-x highlight-changes-rotate-faces - rotate different "ages" of changes
through various faces.
M-x highlight-compare-with-file - mark text as changed by comparing this
buffer with the contents of a file
M-x highlight-compare-buffers highlights differences between two buffers. (fn &optional ARG)