def has_navigation(node, key=None):
"""Returns ``True`` if the node has a :class:`.Navigation` with the given key and ``False`` otherwise. If ``key`` is ``None``, returns whether the node has any :class:`.Navigation`\ s at all."""
try:
def has_navigation(node, key=None):
"""Returns ``True`` if the node has a :class:`.Navigation` with the given key and ``False`` otherwise. If ``key`` is ``None``, returns whether the node has any :class:`.Navigation`\ s at all."""
try: