Show warnings in the Problems view if restrictions are not followed

[ultraq]

The restrictions a dialect developer imposes through the <restrictions> element only prevent the suggestion from showing-up if content assist is invoked. This doesn't actually prevent a developer from typing a processor manually.

If a developer does use a processor 'incorrectly', can I display a warning in the Eclipse Problems view to highlight that there might be a problem with the processor usage? This will be useful in enforcing what the dialect developer intended when they added the restriction in the first place.