Zhelyazko Chobantonov I understand your point but there is a big difference: there is no ambiguity for the compiler as you imported the right constraint annotation. It's not something like "I try this class and if it can't be found I try another one": it only tries the one imported.

In XML, there would be an ambiguity as you would try several classes until you find an existing one and I don't think introducing such ambiguity in the XML support would be a good idea.