More-liberal block-matching

%r{
      ^                                             # Start of line
      <(#{LooseTagPattern}) # start tag: \2
      \b                                            # word break
      (.*\n)*?                              # Any number of lines, minimal match
      .*</\1>                                       # Anything + Matching end tag
      [ ]*                                  # trailing spaces
      $                                             # End of line or document
}ix