code: public void attachUI(final WComponent ui) {
  		if (backing == null || backing instanceof WComponent) {
  			backing = ui;
  		} else if (backing instanceof InterceptorComponent) {
  			((InterceptorComponent) backing).attachUI(ui);
  		} else {
  			throw new IllegalStateException(
  					"Unable to attachUI. Unknown type of WebComponent encountered. " + backing.
  					getClass().getName());
  		}
  	}
docs: Add the WComponent to the end of the interceptor chain.
  
  @param ui the WComponent to add.