US spelling serialisation

I note that Dave switched my attempt at US spelling
  "serialization" to "serialisation"
http://cvs.ilrt.org/cvsweb/redland/rdfcore/syntax/index.html.diff?r1=1.137&r
2=1.133

two questions:
1: what is the correct US spelling of this word?
2: should W3C recs be in en-US or is en-GB acceptable?


Anyone else remember the Unix man page for "spell" I think it was - with the
comment in the BUGS section that the British spelling was done by an
American!

Jeremy