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