IMHO, it would make sense to split the org.jboss.tools.common.validation plugin in two separate ones: core + ui:

• the core part would deal with performing the validation (based on the WST Validation Framework)
• the ui part would deal for the preference pages and configuration.

ATM, the CDI validation is performed in the org.jboss.tools.cdi.core plugin, but this drags a log of .ui dependencies, which is somehow wrong.
OTOH, the JAX-RS validation is performed in the org.jboss.tools.ws.jaxrs.ui plugin to avoid having *.ui dependencies in the org.jboss.tools.ws.jaxrs.core plugin, but this is somehow wrong, too (I had to move the marker declaration in the org.jboss.tools.ws.jaxrs.core plugin to be able to remove all markers when the JAX-RS support is removed from a project, whatever the way it is removed (nature, facet, etc.)

Can we discuss about that change for JBoss Tools 4.3 ?