addSchema(schema, // If array is passed, `key` will be ignored
key, // Optional schema key. Can be passed to `validate` method instead of schema object or id/ref. One schema per instance can have empty `id` and `key`.
_meta, // true if schema is a meta-schema. Used internally, addMetaSchema should be used instead.
_validateSchema = this.opts.validateSchema // false to skip schema validation. Used internally, option validateSchema should be used instead.