code: def _font_of_mention(m):
      
      for ch in m:
          if isinstance(ch, LTChar) and ch.get_text().isalnum():
              return (ch.fontname, _font_size_of(ch))
      return (None, 0)
docs: Returns the font type and size of the first alphanumeric
      char in the text or None if there isn't any.