def line_parse(s):
        """ Given "#+BEGIN: clocktable :maxlevel 3", return
        "#+BEGIN:" und "clocktable :maxlevel 3"
        """
        # has this a keyword?
        assert s[0] == "#"
        assert ":" in s
        bits = s.split(":")
        return bits[0] + ":", (":".join(bits[1:])).lstrip()