The metaschemas are useful but not strict enough. They don't set `additionalProperties: false`, which is great if you wanna extend the schema with your own properties, but it won't catch simple typos.

For example, the following issues pass under the metaschema.

    {"foo": {"bar": { ... }}}  # wrong
    {"foo": {"type": "object", "properties": {"bar": { ... }}}} # correct

    {"additional_properties": false} # wrong
    {"additionalProperties": false} # correct