The sections added to the GNU FDL document have nothing
to do with "fair
use"; they are original work.
You misunderstand, I wsa trying to give an example which the "fair
use" doctrine could be used to exploit the GNU FDL. I could write a
document on my computer and then incorporate parts of that document as
"fair use" into the GNU FDL articles, no-one else would then be able to
modify those sections as they wouldn't be licenced under the GNU FDL.
Let me see if I'm misunderstanding this correctly! Are you suggesting
that you could take an extract from your own previously unpublished
original work and claim that the extract was subject to "fair use"
rules? IMHO it seems that fair use doesn't apply because you already
have the permission of the original author.