Conditional Schema

Suppose I want to support an abstract payload that uses another field to drive nested validations:

TEST_TASK = {
    "folder": {
        "required": True
    }
}

BUILD_TASK = {
    "environment": {
        "allowed": ["staging", "product"]
    }
}

ABSTRACT_TASK = {
    'type': {
        'allowed': ['test', 'build']
    },
    'data': {
        'type': 'dict',
        'required': True,
        'anyof': [
            {'schema': TEST_TASK},
            {'schema': BUILD_TASK}
        ]
    }
}

>>> validator = cerberus.Validator(schemas.ABSTRACT_TASK)
>>> validator.validate({
    "type": "build",
    "data": {
        "environment": "bad"
    }
})
>>> pp validator.errors
{'data': {'anyof': 'no definitions validated',
      'definition 0': {'environment': 'unknown field',
                       'folder': 'required field'},
      'definition 1': {'environment': 'unallowed value bad'}}}

Is there a way to conditionally use definition 1 when the parent has a type of build? For example, if the ABSTRACT_TASK is modified so that anyof is replaced with the BUILD_TASK schema:

>>> pp validator.errors
{'data': {'environment': 'unallowed value bad'}}

[funkyfuture]

what about such constructs?

field: {'if': {rule: constraint, …},
        'then': {rule: constraint, …},
        'else': {rule: constraint, …}
       }

[funkyfuture]

or?

field: {'case': {condition_schema1: conditional_schema1}, 
                {'condition_schema2: conditional_schema2}}