I am actually looking for a decent UML editor. So I create a class, click it, expecting to get at the very least a couple of text areas labeled "Methods" and "Fields." Instead, I get a WYSIWYG editor that looks like it came out of the early 2000's. My immediate reaction was to jump back and shout "DAAAAAA!" (I am not joking about that.)
Now, obviously I don't know exactly what your target audience for this is. But in general, my experience is that if you provide a WYSIWYG editor, the users will do horrible, horrible things to your content. They are usually prone to glitching out in addition. And more specifically, for editing UML, a WYSIWYG editor is just about worthless - it provides no structure to the data, and it makes it incredibly easy to bork up the structure of the class. (Also, the editor doesn't really mesh with your site's design very well.)
So, my advice would be to provide a bit more structure to the content of individual diagram elements (at the very least, separate text boxes for Name, Methods, and Fields in a UML class), and find a less obtrusive WYSIWYG editor if you decide to continue going down that route.
OTOH, I found adding properties and methods using the text editor to be much quicker than the clicking/tabbing around in a dialog box which is the way it's done in UML editors I've used. So I don't know what the right balance is.
What killed it for me, for UML, is that the properties and methods don't have their own connector points for attaching an arrow to.
Now, obviously I don't know exactly what your target audience for this is. But in general, my experience is that if you provide a WYSIWYG editor, the users will do horrible, horrible things to your content. They are usually prone to glitching out in addition. And more specifically, for editing UML, a WYSIWYG editor is just about worthless - it provides no structure to the data, and it makes it incredibly easy to bork up the structure of the class. (Also, the editor doesn't really mesh with your site's design very well.)
So, my advice would be to provide a bit more structure to the content of individual diagram elements (at the very least, separate text boxes for Name, Methods, and Fields in a UML class), and find a less obtrusive WYSIWYG editor if you decide to continue going down that route.