We have an on-call rotation in which one person has the job of cutting (and testing) the internal named release. That person has final choice for the name, often subject to lobbying by the more rap-enlightened members of the team.
/me was pushing for C = Common
I ask because while it is not listed on the github wiki[1] but does appear in the manual[2]. I'm assuming the manual is an oversight, branched from PHP's manual and not pruned.
That said, weak-references are indispensable for certain problems, and I'd love to see them standard.
[1] https://github.com/facebook/hhvm/wiki/Extensions [2] http://docs.hhvm.com/manual/en/book.weakref.php