def to_dict(self):
''' Convert the panel group to a dictionary. '''
d = VirtualPanel.to_dict(self)
children = []
for c in self._children:
if isinstance(c, Panel):
idx = None
for i, p in enumerate(self.root()._container):
if c.is_(p):
idx = i
break
assert(idx is not None)
children.append({ "panel" : idx })
else:
children.append(c.to_dict())
d['children'] = children
return d
