Re: datatypes in Elisp Info: mention "things" for which there is no "thing" datatype - e.g. faces

[Richard M. Stallman]

    But I wonder if perhaps something about this shouldn't be mentioned in the
    Info section on datatypes - perhaps mentioning `face' as an example of
    something you might in some ways be inclined to think of as a datatype but
    that Emacs treats differently from a type.

Adding a brief section about faces in that chapter is a good idea.
I don't have time to work on it, but if someone else writes it,
we could install it.

    2) Cross-reference the discussions of some of the important "non-types",
    such as `face'.

My memory doesn't recall any others, but I wouldn't want to rely on it.
What others do you know of?