Re: Bugs caused by recent use of define-derived-mode

[Richard Stallman]

    As it stands right now, define-derived-mode makes a new abbrev-table
    and then tries to make that new abbrev table "inherit" from the parent
    abbrev-table using a copying mechanism.  This mechanism has various
    flaws, including outright bugs, that are difficult to fix.

If a user manually creates a separate abbrev table for Mail mode, I
think he will find it easy to understand the results of initializing
it as a copy of the Text mode abbrev table.  As a form of
"inheritance", it is inadequate, but if thought of as "copying", the
user will think it works fine.

So I think we should provide a function copy-abbrev-table which the
user could call to make a copy of text-mode-abbrev-table for use in
Mail mode.