speaking as an old regexp wizard from before perl5, this is indeed a great trick, have an upvote.

sadly, this trick still requires a code comment to explain. Python example:

  # match tarzan but not "tarzan"
  # see https://news.ycombinator.com/item?id=27774584
  if "tarzan" == re.search(r'"tarzan"|(tarzan)', myvar)[1]:
     ...

which in practice means it probably deserves a function:

  if re_search_but_exclude(r'tarzan', myvar, '"tarzan"'):
     ...

I don't recommend monkeypatching re, i.e. re.search_but_exclude = ...