I can create a `Layout` with a `yaxis2` attribute using the following methods: ```python layout1 = go.Layout(yaxis2={'title': 'y2'}) layout2 = go.Layout() layout2.yaxis2 = {'title': 'y2'} layout3 = go.Layout() layout3['yaxis2'] = {'title': 'y2'} ``` but not like this: ```python layout4 = go.Layout() layout4.update(yaxis2={'title': 'y2'}) layout5 = go.Layout() layout5.update({'yaxis2': {'title': 'y2'}}) ``` because only `xaxis` and `yaxis` are valid properties for a `Layout` in the schema, so I get a `ValueError`.