'Start of sequence scope
Create a new sequence from the builder and then handle in the context
of its parent.
Args:
event: SequenceStartEvent generated by loader.
loader: Loader that generated event.'

def SequenceStart(self, event, loader):

    self._HandleAnchor(event)
    (token, parent) = self._top
    if (token == _TOKEN_KEY):
        (token, parent) = self._stack[(-2)]
    sequence = self._builder.BuildSequence(parent)
    self._HandleValue(sequence)
    self._Push(_TOKEN_SEQUENCE, sequence)
