I just saw this story over at slash­dot.

“There’s some con­sid­er­able argy-bargy in pro­gress over whether or not GNU’s own GFDL is a Free doc­u­ment­a­tion license at all. At issue are “invari­ant sec­tions” which can­not be removed from deriv­at­ive works.”

It took me about 60 seconds to read the rel­ev­ant por­tion of the GFDL to see that someone has the wrong end of the stick.

“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. (Thus, 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.
The “Invari­ant Sec­tions” are cer­tain Sec­ond­ary Sec­tions whose titles are des­ig­nated, as being those of Invari­ant Sec­tions, in the notice that says that the Doc­u­ment is released under this License. If a sec­tion does not fit the above defin­i­tion of Sec­ond­ary then it is not allowed to be des­ig­nated as Invari­ant. The Doc­u­ment may con­tain zero Invari­ant Sec­tions. If the Doc­u­ment does not identify any Invari­ant Sec­tions then there are none. ”

In other words if, for example, you were to write a book entitled “Hack­ing The GIMP”, license it under the GFDL, and include a sec­tion stat­ing “The author is not a developer of the GIMP and can­not guar­an­tee that your copy of the pro­gram will con­tinue to work after fol­low­ing the instruc­tions in this book.”, you could declare that sec­tion as invari­ant. This seems per­fectly reas­on­able to me.
Without the invari­ant sec­tion a later author could take your work and modify that sec­tion to read “The author guar­an­tees your GIMP will run faster and bet­ter after read­ing this book.” A trivial example, but without the abil­ity to mark the given sec­tion that “deals exclus­ively with the rela­tion­ship of the pub­lish­ers or authors of the Doc­u­ment to the Document’s over­all sub­ject (or to related mat­ters)” as invari­ant a more ser­i­ous sub­ject mat­ter could land an author in a lot of trouble as a res­ult of someone’s (legal) modi­fic­a­tion of the text.