Gregory Maxwell wrote:
If the intention is for mediawiki to not be copylefted, why is it using the GPL at all? Better to not rely on a dodgy corner case of the license.
I suppose you mean copyleft as in the viral clause, thus excluding BSD-style licenses and PD. Lee Daniel Crocker and Erik Moeller explicitly gave all their work on MediaWiki to PD, and I prefer a less restrictive license for new projects. Copyleft isn't "the intention", it's the lowest common denominator. All direct contributors are happy for their work to be distributed under the GPL, and many are happy for it to be distributed without any restriction. Many indirect contributors have a similar policy.
FCKEditor, for example, seems to be the source of most of the reported 253 MPL files. But its standard file header is actually a multiple licensing statement, with GPL, LGPL and MPL.
A PHP license header is put on the top of PHP extension files automatically by the skeleton generator, complete with a bogus copyright claim "Copyright (c) 1997-2003 The PHP Group". It generally doesn't reflect a deliberate choice by the author.
I haven't been able to find the purported Apache License, Artistic License or CDDL files.
The GPL, being by far the most restrictive free license, seems to be for people who have reservations about giving their code away. The GPL seeks to maintain a sense of ownership and control, by restricting many kinds of derivative reuse and by mandating attribution. I'm not going to be bullied into making it my preferred license for new code.
-- Tim Starling