I re-enabled the Wicket annotations created by Petr Pisl (all the way back in 2006!) and enhanced by Tim Boudreau. Since I'm now on the product marketing side of things, with my marketing hat on I think the feature would be well positioned under the title "Visual Wicket Parsing". There's nothing you need to do to enable this feature, though you can customize its coloring in the Options window. Below you see its default colors, I decided to not choose red because that would indicate a compiler error, but something softer and also Wicketier, which is clearly orange:
And what does the Visual Wicket Parser do? Well, here's an example:
If you save the document, another parse is done, and the annotation will disappear, if the IDs now match. Other than the above, you will be informed on the other side, i.e., in the Java file as well. In other words, both sides of the Wicket component show the above annotation. And other parsing is done too, to check whether the ID has already been used at the same level, i.e., duplicate IDs, and whether an ID exists on one side but not on the other.
Currently this feature is in the repo on java.net, not yet in a released binary.