private void alterPriority(ICompletionProposal proposal, int delta) {
   if (proposal == null || !(proposal instanceof ConfigurableCompletionProposal)) return;
   ConfigurableCompletionProposal castedProposal = (ConfigurableCompletionProposal) proposal;
   castedProposal.setPriority(castedProposal.getPriority() + delta);
 }