docs: def parse (cls, line, lineno, log, cmddict=None):
      """Parses the SeqMetaCmd from a line of text.  Warning and error
      messages are logged via the SeqMsgLog log.
      """
      start  = line.find('%')
      pos    = SeqPos(line, lineno, start + 1, len(line))
      result = None
  
      if start >= 0:
        result = cls(line[start:], pos)
  
      return result