code: public List getFeedback()
  	    {
  	        List<?> messages = new ArrayList();
  	        for ( ValueSource vs : valueSources )
  	        {
  	            List feedback = vs.getFeedback();
  	            if ( feedback != null && !feedback.isEmpty() )
  	            {
  	                messages.addAll( feedback );
  	            }
  	        }
  
  	        return messages;
  	    }
docs: Return any feedback messages and errors that were generated - but
  suppressed - during the interpolation process. Since unresolvable
  expressions will be left in the source string as-is, this feedback is
  optional, and will only be useful for debugging interpolation problems.
  
  @return a {@link List} that may be interspersed with {@link String} and
  {@link Throwable} instances.