Hi,
we use for the guides the "Creative Commons Attribution License, version 3.0 or later". Version 3.0 sems to be obsolete now, being replaced by the Creative Commons Attribution 4.0 International license <http://creativecommons.org/licenses/by/4.0/>.
Perhaps we should change it. I think that the main difference is the "International" - while in 3.0 it was expected that the CC licenses would be adapted for the local conditions in different countries, 4.0 should be "one size fits all" - with no required adaptation.
best
Milos