David Goodman wrote:
do they copy as a mirror would, and then add articles of their own, or do they use the text as part of articles with additions & subtractions of their own?
I believe it's the latter. They are of course free to edit as they will; that's allowed even if the editing is grossly distorted. Another important feature of GFDL is the viral effect that incorporating licensed material will have on the copyright of the new usage.
Ec