docs: def create_slug(title, plain_len=None):
      '''
      Tries to create a slug from a title, trading off collision risk with readability and minimized cruft
  
      title - a unicode object with a title to use as basis of the slug
      plain_len - the maximum character length preserved (from the beginning) of the title
  
      >>> from versa.contrib.datachefids import create_slug
      >>> create_slug(u"The  quick brown fox jumps over the lazy dog")
      'the_quick_brown_fox_jumps_over_the_lazy_dog'
      >>> create_slug(u"The  quick brown fox jumps over the lazy dog", 20)
      'the_quick_brown_fox'
      '''
      if plain_len: title = title[:plain_len]
      pass1 = OMIT_FROM_SLUG_PAT.sub('_', title).lower()
      return NORMALIZE_UNDERSCORES_PAT.sub('_', pass1)