these are not implemented yet and throw an error. We are hitting these errors on Wikidata on some items with these values.

This especially happens with values that are for some reason valid or can be handled in the backend but not in the frontend. An example of this is a time value with precision higher than a day.

also, the implementation of this value stores a JavaScript Error object for _unserializeError. In the php implementation, this part of the value is just a string (the error message). We may want to make that consistent, and would more simple to implement toJSON and newFromJSON for the value and to interact with backend code via the api.