Re: buffer-modified indicator in mode line - distinguish savable from unsavable changes

[Richard Stallman]

    An example of a type 1 change is typing or deleting text. An example of a
    type 2 change is changing the face of a some text (e.g. using the facemenu).

In the future, we want to be able to save text properties.  However,
in most buffers that is impossible.

buffer-modified-p could, in principle, consider text property changes
insignificant in buffers that cannot save them.  It is something to consider
trying out after the release.