I do not think it is a good idea. It does not matter what value you get from Prosemirror or any editor, Yjs provides shared types and they should follow web standards. According to Web API, XML attribute values must always be quoted. That is why it should be always a string.

Well, MDN states for setAttribute that Value: A string containing the value to assign to the attribute. Any non-string value specified is converted automatically into a string. https://developer.mozilla.org/en-US/docs/Web/API/Element/setAttribute That change is in the toDOM method (though only for number).

Additionally, note that this case came up in the first place because we're cloning an existing element which already had somehow managed have a number as the value type. So one could just as easily argue that things should have already broken upstream when the doc/elements were created. At a minimum, there's a big difference in the behavior between creating elements and cloning them.