Any contributions I make to existing pages I agree to licence under whatever licence is currently in force for that page.
My own contributions I place under the Gnu Free Documentation Licence, and see below.
Licensing rights granted to Wikimedia Foundation
I grant non-exclusive permission for the Wikimedia Foundation Inc. to relicense my text contributions under any copyleft license that it chooses, provided it maintains the free and open spirit of the GFDL. This permission acknowledges that future licensing needs of the Wikimedia projects may need adapting in unforeseen fashions to facilitate other uses, formats, and locations. It is given for as long as this banner remains.