docs: def _is_broken_ref(key1, value1, key2, value2):
      """True if this is a broken reference; False otherwise."""
      # A link followed by a string may represent a broken reference
      if key1 != 'Link' or key2 != 'Str':
          return False
      # Assemble the parts
      n = 0 if _PANDOCVERSION < '1.16' else 1
  
      if isinstance(value1[n][0]['c'], list):
          # Occurs when there is quoted text in an actual link.  This is not
          # a broken link.  See Issue #1.
          return False
  
      s = value1[n][0]['c'] + value2
      # Return True if this matches the reference regex
      return True if _REF.match(s) else False