My assumption as a modeler would be that you can save anything in an A12 Document as long as the data matches the data type and data type configuration for the respective Document Model.
…and this is true.
So the general statement is:
In general:
Everyone is responsible for his specific data handling, regardless it’s image in quoted printable, XML, HTML, or any other inner format. In DS they are content agnostic, so whatever is modelled is applied, but specific customizations requires extra code, hooked to events for example.
I recently posted in Persisting Rich Text Editor State