In memory orm.
see doc-users.md (use doc-users.py to modify)
Field validation is based on Marshmallow v2.x framework.
new marshmallow release https://marshmallow.readthedocs.io/en/stable/upgrading.html https://github.com/marshmallow-code/marshmallow/commit/5af0df42b3eaed23f53af923917b27d01f0add51