Sorry, I overlooked an escaped backslash. Try this:
--langdef=ActionScript --langmap=ActionScript:.as --regex-ActionScript=/^[ \t]*[(private|public|static)( \t)]*function [ \t]+([A-Za-z0-9_]+)[ \t]*(/\1/f,function,functions/ --regex-ActionScript=/^[ \t]*[(public)( \t)]*function[ \t]+(set|get) [ \t]+([A-Za-z0-9_]+)[ \t]*(/\2/p,property,properties/ --regex-ActionScript=/.*.prototype.([A-Za-z0-9 ]+)=([ \t]?) function([ \t]?)*(/\1/f,function,functions/
This works a treat. Thanks Gerd !