Techniques for WCAG 2.0

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FLASH12: Providing client-side validation and adding error text via the accessible description

Important Information about Techniques

See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.0 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.0.


This technique relates to:

User Agent and Assistive Technology Support Notes

See User Agent Support Notes for FLASH12. Also see Flash Technology Notes.


The objective of this technique is to validate user input as values are entered for each field, by means of client-side scripting. If errors are found, a description is added to the controls that have invalid data. Visually, the description will be placed adjacent to the control. Additionally, the error message text is added to the control's accessible description so that it is readable by assistive technology when the control receives focus.


Example 1: Validating a text field

In this example, a sample form is shown with two text fields ('name' and 'zip code'). Both fields are required. When the form's submit button is pressed, the values of the text fields will be validated. If a textfield contains an invalid value, an _accProps object is created for the textfield, and its description property is set the error message.

Note: Instead of using the accessible description, the error text can also be added to the accessible name (, which is supported by a wider range of assistive technology than the _accProps.description property.

ActionScript 2.0 Code

Example Code:

import flash.accessibility. *;
import mx.accessibilty.ButtonAccImpl;
import mx.controls.Alert;
import mx.accessibility.AlertAccImpl;



submit_btn.addEventListener("click", handleClick);
function handleClick(e) {
  //reset values
  //perform validation
  var errors =[];
  if (name_txt.text == '')
    errors.push([name_txt, "You must enter your name", name_error_lbl]);
  if (zipcode_txt.text == '')
    errors.push([zipcode_txt, "You must enter your zip code", zipcode_error_lbl]);
  else if (zipcode_txt.text.length != 5 || isNaN(zipcode_txt.text))
    errors.push([zipcode_txt, "Zip code must be 5 digits", zipcode_error_lbl]);
  //add validation error messages, if any
  var field, errorMsg, errorLabel;
  if (errors.length > 0) {
    //loop over encountered errors
    for (var i = 0; i < errors.length; i++) {
      field = errors[i][0];
      errorMsg = errors[i][1];
      errorLabel = errors[i][2];
      updateAccDescription(field, "Warning: " + errorMsg);
      errorLabel.text = errorMsg;
  } else {"Form field values were entered correctly");

function updateAccName(obj, newName: String) {
  if (! obj._accProps)
  obj._accProps = new Object(); = newName;

function updateAccDescription(obj, newDescription: String) {
  if (! obj._accProps)
  obj._accProps = new Object();
  obj._accProps.description = newDescription;

function getAccName(obj) {
  return obj._accProps? "";

function resetTextFieldAccNames() {
  updateAccName(name_txt, "name, required");
  updateAccName(zipcode_txt, "zip code, required");

function resetTextFieldAccDescriptions() {
  updateAccDescription(name_txt, "");
  updateAccDesciption(zipcode_txt, "");

function resetErrorLabels() {
  name_error_lbl.text = "";
  zipcode_error_lbl.text = "";

This approach is demonstrated in working version of Validating a text field. The source of Validating a text field is available.



When a Flash movie provides interactive forms that can be submitted, confirm that:

  1. The validation warnings are placed next to the control visually.

  2. The validation warnings are added to the accessible name or description of each control.

Expected Results

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.