@classmethod
def schema(cls):
    """Return a json-schema for the plugin's properties as a dictionary.
        Of importance to plugin authors is the 'properties' keyword and
        optionally the 'requires' keyword with a list of required
        'properties'.

        By default the properties will be that of a standard VCS,
        override in custom implementations if required.
        """
    return {'$schema': 'http://json-schema.org/draft-04/schema#', 'type':
        'object', 'additionalProperties': False, 'properties': {},
        'pull-properties': [], 'build-properties': [], 'required': []}
