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

[Drew Adams]

        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?

I didn't have any others in mind. I just wanted to speak about this
generally, in case there were others. (Kenichi Handa mentions coding-system,
charset, fontset.)