Distinguish textual modifications from properties-only modifications?

[Bastien]

Changing the text properties makes (buffer-modified-p) to return t.

If a file has been modified outside Emacs after it has been opened
in Emacs, one cannot change the text properties of the buffer without
being asked whether we really want to edit the buffer.

This default looks good to me, but I wonder if there is a way to
get rid of the warning, or to distinguish between text modifications
and properties modifications.

Thanks for any advice,

-- 
 Bastien