This document is a draft, and is designed to show changes from a previous version. It is presently showing added text,changed text,deleted text,[start]/[end] markers,and Issue Numbers.
Changes are displayed as follows:
Server-side technologies, including server-side scripting languages and server configuration files with URLs or URL patterns for redirects.
This technique relates to:
The objective of this technique is to avoid confusion that may be caused
when two new pages are loaded in quick succession because one page (the one
requested by the user) redirects to another. Some user agents support the
use of the HTML meta element to redirect the user to another page
after a specified number of seconds. This makes a page inaccessible to some
users, especially users with screen readers. Server-side technologies
provide methods to implement redirects in a way that does not confuse users.
A server-side script or configuration file can cause the server to send an
appropriate HTTP response with a status code in the 3xx range and a Location
header with another URL. When the browser receives this response, the location
bar changes and the browser makes a request with the new URL.
In Java Servlets or JavaServer Pages (JSP), developers can use
HttpServletResponse.sendRedirect(String url).
…
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
…
response.sendRedirect("/newUserLogin.do");
} This sends a response with a 302 status code ("Found") and a
Location header with the new URL to the user agent. It is also
possible to set another status code with
response.sendError(int code, String message) with
one of the constants defined in the interface
javax.servlet.http.HttpServletResponse as status code.
…
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
…
response.sendError(response.SC_MOVED_PERMANENTLY, "/newUserLogin.do");
} If an application uses HttpServletResponse.encodeURL(String
url) for URL rewriting because the application depends on
sessions, the method
HttpServletResponse.encodeRedirectURL(String url)
should be used instead of
HttpServletResponse.sendRedirect(String url). It is
also possible to rewrite a URL with
HttpServletResponse.encodeURL(String url) and then
pass this URL to HttpServletResponse.sendRedirect(String
url).
In Active Server Page (ASP) with VBScript, developers can use
Response.Redirect.
Response.Redirect "newUserLogin.asp"
or
Response.Redirect("newUserLogin.asp")The code below is a more complete example with a specific HTTP status code.
Response.Clear Response.Status = 301 Response.AddHeader "Location", "newUserLogin.asp" Response.Flush Response.End
In PHP, developers can send a raw HTTP header with the
header method. The code below sends a 301 status code
and a new location. If the status is not explicitly set, the
redirect response sends an HTTP status code 302.
<?php
header("HTTP/1.1 301 Moved Permanently);
header("Location: http://www.example.com/newUserLogin.php");
?>Developers can configure the Apache Web server to handle redirects, as in the following example.
redirect 301 /oldUserLogin.jsp http://www.example.com/newUserLogin.do
Resources are for information purposes only, no endorsement implied.
Use standard redirects: do not break the back button! (W3C QA Tip).
HTTP 301 Permanent Redirection Techniques by Shailesh N. Humbad.
Interface javax.servlet.http.HttpServletResponse in the Java Servlets 2.3 API documentation.
header in the PHP Manual.
Apache Module mod_alias in the Apache HTTP Server Version 2.2 Documentation describes how redirects can be specified in Apache 2.2.
Module mod_alias in the Apache HTTP Server Version 1.3 Documentation describes how redirects can be specified in Apache 1.3.
(none currently listed)
Find each link or programmatic reference to another page or Web page.
For each link or programmatic reference to a URI in the set of Web pages being evaluated, check if the referenced Web page contains code (e.g. meta element or script) that causes a client-side redirect.
For each link or programmatic reference to a URI in the set of Web pages being evaluated, check if the referenced URI does not cause a redirect OR causes a server-side redirect without a time-out.
Step 2 is false AND step 3 is true.
Content residing on a Web server that supports .htaccess (typically Apache) where a conforming version of content is provided as an alternative to a non-conforming version.
This technique relates to:
The objective of this technique is to ensure that users can always access an accessible version of the content when non-conforming versions are also available. Whenever content is provided in a format that does not conform to WCAG, the site as a whole can still conform if alternate versions of the inaccessible content are provided. Conformance Criterion 4 requires that alternate versions can be derived from the nonconforming content or from its URI.
Since it is not always possible to provide an accessible link from within non-conforming content, this technique describes how authors can use Apache's Module "mod_access" to ensure that non-conforming content can only be accessed from URIs that serve as alternate versions to the non-conforming content or from pages that include links to both the non-conforming version and the alternative version.
The following .htaccess file uses Apache's mod_redirect module to redirect requests for "inaccessible.html" to "accessible.html" unless the request comes from "accessible.html".
# If the request for inaccessible content comes from a file
# called accessible.html, then set an environment variable that
# allows the inaccessible version to be displayed.
SetEnvIf Referer .*(accessible.html)$ let_me_in
<FilesMatch ^(inaccessible.html)$>
Order Deny,Allow
Deny from all
Allow from env=let_me_in
</FilesMatch>
# If the request comes from anyplace but accessible.html, then
# redirect the error condition to a location where the accessible
# version resides
ErrorDocument 403 /example_directory/accessible.html
This example assumes a directory structure where documents are available in multiple formats. One of the formats does not meet WCAG at the level claimed and uses the file extension "jna" (Just Not Accessible). All of these files are stored in a folder called "jna" with an .htaccess file which ensures that any direct request for a file with the .jna extension from pages where inaccessible versions are not already available is redirected to an index page that lists all of the available formats.
# If the request for inaccessible content comes from a file at
# http://example.com/documents/index.html, then set an environment
# variable that allows the inaccessible version to be displayed.
SetEnvIf Referer ^http://example.com/documents/index.html$ let_me_in
<FilesMatch ^(.*\.jna)$>
Order Deny,Allow
Deny from all
Allow from env=let_me_in
</FilesMatch>
# If the request comes from anyplace but http://example.com/documents/index.html, then
# redirect the error condition to a location where a link the accessible
# version resides
ErrorDocument 403 http://example.com/documents/index.html
Resources are for information purposes only, no endorsement implied.
Identify pages that do not conform to WCAG at the conformance Level claimed where accessible alternatives are served based on the use of .htaccess files.
Visit the URI of the non-conforming content.
Verify that the resulting page does one of the following:
conforms at the level claimed
includes a link to both the conforming and non-conforming content
Either check #3.1 or #3.2 are true.