I was thinking about custom widgets too (seems like your idea is somehow close to them). Widget here is a class of custom DOM elements that knows how to repres

I was thinking about custom widgets too (seems like your idea is somehow close to them). Widget here is a class of custom DOM elements that knows how to represent itself by HTML means. Such classes constitute that 'library' of yours, AFAIU. When you load document containing such widget, the class instantiated and it can check HTML structure it gets assigned to and morph content if needed. So it is a matter of loading/saving the document to get updated structure.