I'd like to suggest that the zero-width lookbehind and negative
lookbehinds in regular expressions which are:
  (?<=PATTERN) - zero-width positive lookbehind assertion
  (?<!PATTERN) - zero-width negative lookbehind assertion
be included into ruby's Regex. They allow problems such as "How do I
delete all but the first three characters of a string?" to be solved
idiomatically as s/(?<=...).+// and the like in a readable and convienent
way where the currently-existing lookaheads just wouldn't work as well.

Code that I currently have as:
  if line =~ /(?!\\).?#{$splitchar}/
could be so much better and make so much more sense as:
  if line =~ /(?<=\\)#{$splitchar}/
whereas the above version is just hackish and less versatile. (and I
notice now that the first version doesn't even *work*, grr...)

Thank you,