Re: A possible GFDL compromise

[Richard Stallman <rms@gnu.org>]

    Saying "you can modify the documentation, just not the invariant
    sections" isn't enough, incidentally, to answer this, because the
    attachment of the invariant section to the documentation *is* a
    property of the documentation.  (Consider if there were such a thing
    on a piece of software: you can modify all these functions, but not
    that one.  The result is that the whole thing is nonfree.)

This would be like having a technical section which can't be changed.
That would be non-free, but it's not what our actual invariant sections do.

For them, the preamble of the GPL is a better analogy.
That too is text that can't be changed or removed from the program,
but does not restrict its practical functionality.