code: public void register(Delta delta) {
  		final IResourceDescription newDesc = delta.getNew();
  		if (newDesc == null) {
  			removeDescription(delta.getUri());
  		} else {
  			addDescription(delta.getUri(), newDesc);
  		}
  	}
docs: Put a new resource description into the index, or remove one if the delta has no new description. A delta for a
  particular URI may be registered more than once; overwriting any earlier registration.
  
  @param delta
  The resource change.
  @since 2.9