Re: pending-undo-list is not buffer local

[Richard Stallman]

    Like `buffer-file-name'.  Would it make sense to introduce a variable,
    say `buffer-file-name-extension', assign its initial value from
    `buffer-file-name', make it a permanent buffer-local, and hope that the
    value of the new variable always correctly reflects the extension of
    `buffer-file-name' without any additional provisions?

I don't understand what this has to do with.