OptionalcreateOptionaldefaultIf true, allows for values to be stringified without
an explicit tag together with test.
If 'key', this only applies if the value is used as a mapping key.
For most cases, it's unlikely that you'll actually want to use this,
even if you first think you do.
OptionalformatIf a tag has multiple forms that should be parsed and/or stringified
differently, use format to identify them.
OptionalidentifyUsed by YAML.createNode to detect your data type, e.g. using typeof or
instanceof.
The identifier for your data type, with which its stringified form will be
prefixed. Should either be a !-prefixed local !tag, or a fully qualified
tag:domain,date:foo.
An optional factory function, used e.g. by collections when wrapping JS objects as AST nodes.