Re: typo in frame.el

[Richard Stallman]

    I prefer "precisely when" instead of "if and only if".  Sometimes,
    even the "precisely" can be omitted.  Less technobabbly.  Alas,
    changing "iff" into "when" can make a documentation string line too
    long.

I think "precisely when" is a clear way to say it, but just "when"
often is not.