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GPL - "specifying" the preferred form for modification

On Fri, Jan 28, 2005 at 09:49:08PM +0100, Frank Küster wrote:
> Let's assume a piece of technical documentation (standalone, i.e not
> part of a software package; something like selfhtml or LaTeX's lshort),
> is licensed under GPL, with an additional text stating what the
> preferred form for modification is (say, LaTeX or docbook).

If you "specify" what the preferred form of modification is, you're not
using the GPL.  The GPL doesn't say what the preferred form is.  This
is extremely important: I can always take your work--say, a program
written in Pascal--convert it to C, modify it, and discard the Pascal
source, as long as the new C code really is my preferred form for
modification.  (That is, I can't modify a program, wave my hands around
saying "this assembly dump is my preferred form" and only distribute
that--that's just fraudulent.)

(Obviously, the old Pascal code may be useful, but only as documentation,
not source code--that's very different.)

The GPL doesn't lock a work into a particular source form--if you've said
"the preferred form for modification is Pascal", it's not at all clear
what happens when the preferred form has become something else as the
program evolves.  It's also not clear what happens when I link your
Pascal code against my C code when your code effectively says "must
include Pascal source code".  The GPL very deliberately does not specify
the preferred form for modification, and authors shouldn't do so (at
least not in a legally-binding way or an attempt to "interpret" the GPL).
Note, also, that the GPL says "preferred form for modification", not
"the form for modification preferred by the original author".

This has come up several times, so I'm CCing licensing@fsf to get their
take on this.  FSF folks: please ignore the documentation aspect above;
I'm interested in the general problem of people "specifying" the preferred
form for modification, which I believe is tantamount to placing an additional
restriction beyond the GPL.  Let me know if I'm way off base.

Glenn Maynard

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