docs: def is_valid_code_fence_indent(line: str, parser: str = 'github') -> bool:
      r"""Determine if the given line has valid indentation for a code block fence.
  
      :parameter line: a single markdown line to evaluate.
      :parameter parser: decides rules on how to generate the anchor text.
           Defaults to ``github``.
      :type line: str
      :type parser: str
      :returns: True if the given line has valid indentation or False
           otherwise.
      :rtype: bool
      :raises: a built-in exception.
      """
      if (parser == 'github' or parser == 'cmark' or parser == 'gitlab'
              or parser == 'commonmarker'):
          return len(line) - len(line.lstrip(
              ' ')) <= md_parser['github']['code fence']['min_marker_characters']
      elif parser == 'redcarpet':
          # TODO.
          return False