code: private static String encodeVisibility(IResponsive r, String value, String prefix) {
  		if(value == null) return "";
  
  		if ("true".equals(value) || "false".equals(value)) {
  			throw new FacesException("The attributes 'visible' and 'hidden' don't accept boolean values. If you want to show or hide the element conditionally, use the attribute 'rendered' instead.");
  		}
  		List<String> str = wonderfulTokenizer(value, delimiters);
  		return evaluateExpression(str, delimiters, validValues, prefix, r.getDisplay());
  	}
docs: Encode the visible field
  @param r
  @return