I've just heard today that there are people on this list who believe that the GFDL is not DFSG-compliant. The GFDL text very clearly specifies that the invariant sections must be "Secondary" in nature, and then goes on to define secondary sections as follows:
A "Secondary Section" is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (For example, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them. If this makes the GFDL non-DFSG-compatible, then no license that requires that license text, attribution or copyright notices be invariant is DFSG-compliant: which is just about every one of them - even the MIT or BSD license requires that. This is taking the definition to the point of absurdity. The GFDL is a DFSG-compliant license. Thanks Bruce Perens