'Handle anchor attached to event.
Currently will raise an error if anchor is used.  Anchors are used to
define a document wide tag to a given value (scalar, mapping or sequence).
Args:
event: Event which may have anchor property set.
Raises:
NotImplementedError if event attempts to use an anchor.'

def _HandleAnchor(self, event):

    if (hasattr(event, 'anchor') and (event.anchor is not None)):
        raise NotImplementedError('Anchors    not    supported    in    this    handler')
