Used Cerberus 1.1:

I consulted these documentations:
- http://docs.python-cerberus.org/en/stable/
- http://docs.python-cerberus.org/en/latest/
I consulted these sections of the docs (add more lines as necessary):
- http://docs.python-cerberus.org/en/latest/schemas.html#registries
I found nothing relevant to my problem in the docs.
I found the documentation not helpful to my problem.
I have the capacity to improve the docs when my problem is solved.
I have the capacity to submit a patch when a bug is identified.

Use-case abstract

I am trying to add schemas to a custom registry so that I don't clutter the cerberus.schema_registry namespace.
Adding any schema to a newly created Registry object results in an attribute error.

Support request / Bug report

import cerberus
r = cerberus.Registry()
r.add('non-system user', {'uid': {'min': 1000, 'max': 0xffff}})

results in

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-20-ad8c4bb8a5d2> in <module>()
----> 1 r.add('non-system user', {'uid': {'min': 1000, 'max': 0xffff}})
~/anaconda/envs/athion-forecaster/lib/python3.6/site-packages/cerberus/schema.py in add(self, name, definition)
    375         :param definition: The definition.
    376         :type definition: any :term:`mapping` """
--> 377         self._storage[name] = self._expand_definition(definition)
    378
    379     def all(self):
AttributeError: 'Registry' object has no attribute '_expand_definition'