EdX measures and evaluates accessibility using the World Wide Web Consortium’s Web Content Accessibility Guidelines (WCAG) 2.0 (Dec. 11, 2008). All features that you merge into edX repositories are expected to conform to Level AA of this specification and to satisfy the requirements outlined in the edX Website Accessibility Policy.
The edX Accessibility Guidelines are intended to extend the guidance available in WCAG 2.0, with a focus on features frequently found in the Open edX platform, as well as in Learning and Content Management Systems in general.
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The core mission of edX is to expand access to education for everyone. We expect any user interfaces that are developed for the Open edX platform to be usable by everyone, regardless of any physical limitations that they might have. The Open edX platform is used every day by people who might not be able to see or hear, or who might not be able to use traditional modes of computer interaction such as the mouse or keyboard.
Understanding a few core concepts about how people with disabilities use the web and web applications should give you more context for applying the guidance in this document.
Keep these core concepts in mind when you develop user interfaces, so that they can truly be used by everyone. More information is available from the W3C’s Web Accessibility Initiative’s publication How People with Disabilities Use the Web: Overview.
The following sections cover some best practices and tips to keep in mind as you develop user interfaces that are WCAG 2.0 compliant.
The role, state, and associated properties of an element are exposed to users of assistive technologies either directly through the DOM (Document Object Model) or through the Accessibility API. If you use elements for purposes other than their intended purposes, you can “break” features that are designed to make web applications easier to use, resulting in confusion when expected behaviors are not available. For example, the role, state, or associated properties of an element might be incorrectly reported when you use an element in a way that it was not designed to be used, causing confusion for users who rely on assistive technologies.
If the semantics and behavior you need already exist in a native HTML5 element, you should use that element. Do not use an element because of its default style or because it provides a convenient styling hook. Here are some common examples.
If you want a checkbox, use the
<input type=checkbox> element. Do not try to
recreate states and properties that are included with the native element, such
as focus or state. If you attempt to do so, more than likely you will not fully
replicate all of them. Native checkbox elements include a toggle for checked
enter keypresses, exposing its label and
the Accessibility API.
Use the appropriate levels of headings (
h6>) to denote a logical
hierarchical order of content. Do not use headings as stylistic markup (for
their physical size or appearance).
Use ordered lists (
<ol>) only when you are marking up a collection of
related items whose order in the list is important. Use unordered lists
<ul>) only when you are marking up a collection of related items. Screen
readers provide extra feedback and functionality for lists and other elements
with semantic importance. It can be confusing or cumbersome when this feedback is
You can make images accessible by using the
alt attribute for each image, or
by providing a text alternative for an image.
For users who are unable to view or use non-text content (such as images, charts, applets, audio files and so on), you can provide a text alternative . A text alternative is text that non-sighted users can access in place of the non-text content.
Text alternatives must be “programmatically determinable”. This means that the assistive technologies and accessibility features in browsers must be able to read and use the text.
Text alternatives must also be “programmatically associated” with the non-text content. This means that users must be able to use assistive technology to find the text alternative when they land on the non-text content.
All images require a text alternative. The only exceptions to this rule are purely decorative images or images that have text alternatives adjacent to them.
Regardless of whether or not an image requires a text alternative, you must
alt attribute for all
<img> elements, even if the value of
that attribute is empty (
alt=""). An empty
alt attribute is also called
If your image is purely decorative, or has a text alternative immediately adjacent to it, use a NULL
<img> element does not have a NULL
alt attribute, you should make
sure that the value you use in its
alt attribute provides useful information
to users who rely on screen readers. If an
alt attribute value does not
exist, screen readers will expose the path to the image as a last resort.
Providing useful text alternatives or
alt attribute values is more difficult
than it sounds. Ask yourself questions about the purpose of your image to
determine what would be most useful to the user.
Is your image the only content of a link or form control?
altattribute should describe the destination of the link, or the action that will be performed. For example, a “Play” icon should have a text alternative such as “Play the ‘Introduction to Linux’ course video”, rather than “Right-pointing triangle”.
Does your image contain text? The vast majority of images of text should
include the verbatim text as the value of the
alt attribute. Here are some
examples of exceptions.
- If yes, and if the same text appears adjacent to or near the image in the DOM, use a NULL value in the
altattribute, otherwise a screen reader is exposed to the same content twice.
- If yes, and if the text within the image is there simply for visual effect (such as a skewed screenshot of computer code), use a NULL value in the
Does your image contribute meaning to the current page or context?
- If yes, and if the image is a simple graphic or photograph, the
altattribute should briefly describe the image in a way that conveys the same meaning that a sighted person would obtain from viewing the image. Context is important. A detailed description of a photograph is rarely useful to the user, unless it is in the context of a photography or art class.
- If yes, and if the image is a graph or complex piece of information, include the information contained in the image elsewhere on the page. The
altattribute value should give a general description of the complex image. You can programmatically link the image with the detailed information using
A pragmatic guide on providing useful text alternatives is included in the HTML5 specification (18.104.22.168). It provides a variety of example images and appropriate text alternatives.
A more comprehensive decision tree is available in the Web Accessibility Initiatives Images Tutorial.
CSS-generated content can cause many accessibility problems. Since many screen readers interact with the DOM, they are not exposed to content generated by CSS, which does not live in the DOM. There is currently no mechanism for providing alternative content for images added using CSS (either background images or pseudo elements).
Many developers think that providing screen reader-only text can be used to solve this problem. However, images added using this technique are not rendered to users who have high contrast mode enabled on their operating systems. These users are likely not using screen readers, so they cannot access the visible icon or the screen reader text.
When adding images that represent important navigational or information
<img> elements with appropriate
alt attributes. For more
information about making images accessible, see Make images accessible.
title attribute to provide a description of the embedded content to
help users decide whether or not they would like to interact with this content.
It is possible that
<iframe> titles are presented out of context (such as in
a list within a dialog box), so choose title text that will make sense when it
is exposed out of context.
Sighted users have the benefit of visual context. It is usually quite obvious to
them what the purpose is of a given form field, based on physical proximity of
descriptive text or other visual cues. However, to a user with a vision
impairment, who does not have the benefit of visual context, these relationships
are not obvious. Users who rely on speech to interact with their computers also
need a label for addressing form elements. If you correctly use the
element, text is programmatically associated with a given form element, and can
then be read to the user upon focus, or used to address the form element using
Screen readers often enter “forms processing mode” when they encounter
a form. This mode temporarily disables all keyboard shortcuts available to
users so that key presses are passed through to the control. The exception is
TAB key, which moves focus from one form field to the next. This
means that context-sensitive help provided for form fields (such as UI help
text adjacent to the form field) is not likely to be encountered by screen
reader users. To remedy this situation, add an aria-describedby
attribute to the input that references the help text. Doing so
programmatically links the help text to the form control so that users can
access it while their screen readers are in forms processing mode.
WAI-ARIA (Web Accessibility Initiative - Accessible Rich Internet Applications) is a technical specification published by the World Wide Web Consortium (W3C) that specifies how to increase the accessibility of web pages.
When you develop custom widgets, use WAI-ARIA to ensure that your custom controls are accessible, and consider the following points.
Adding an ARIA
role overrides the native role semantics reported
to the user from the Accessibility API. ARIA indirectly affects what is
reported to a screen reader or other assistive technology. Adding an ARIA
role to an element does not add the behaviors or attributes to that
element. You have to do that yourself.
ARIA attributes can also be used to enhance native elements by adding helpful
information specifically for users of assistive technology. Certain sectioning
elements (such as
<header>) as well as generic ones (such as
<div> with “search”, “main” or “region” roles defined), receive special
behaviors when encountered by assistive technology. Most screen readers announce
when a user enters or leaves one of these regions, allow direct navigation to
the region, and present the regions to a user in a list that they can use to
browse the page out of context. Because your pages are likely to have multiple
<nav> elements or
<div> elements with “region” roles defined, it is
important to use the
aria-label attribute with a clear and distinct value to
differentiate between them.
<!-- the word "Navigation" is implied and should not be included in the label --> <nav aria-label="Main"> ... </nav> <nav aria-label="Unit"> ... </nav> <div role="search" aria-label="Site"> ... </div> <div role="search" aria-label="Course"> ... </div>
The following list outlines specific cases in which you have to be careful using WAI-ARIA.
role="presentation" strips away all of the semantics from a native
role="application" on an element passes all keystrokes to the
browser for handling by scripts. In this case, all keyboard shortcuts provided
by screen readers are disabled. You should only use
you can provide support for all of the application’s functions via the
keyboard as well as the roles, states, and properties for all of its child
aria-hidden="true" removes an element from the Accessibility API,
making it invisible to a user of assistive technology. For elements that you
intend to hide from all users, setting the CSS property
sufficient. It is unnecessary to also set
aria-hidden="true". Once the
content is revealed by changing the display property, it is too easy to forget
to toggle the value of
There are legitimate use cases for
aria-hidden, for example when you use
an icon font that has accessible text immediately adjacent to it. Icon fonts
can remain silent when focused on by certain screen readers, which can lead
users of screen readers to suspect that they are missing important content.
Icon fonts can also be rendered as nondescript glyphs by some screen readers
that display what is being spoken on the screen. In these cases, it is useful
to remove icon fonts using
aria- hidden, so that screen reader users are
not provided with the same information in both accessible and less-accessible
Additional considerations for developing custom widgets are covered in General steps for building an accessible widget.
Specific considerations for common widgets are covered in WAI-ARIA 1.0 Authoring Practices - Design Patterns.
A quick reference list of Required and Supported ARIA attributes by role is available in the ARIA Role, State, and Property Quick Reference
Do not forget to manage focus on pop-ups. Whenever a control inserts interactive content into the DOM or reveals previously hidden content (for example, pop-up menus or modal dialog boxes), you must move focus to the container. While the focus is within the menu or dialog box, keyboard focus should remain trapped within its bounds. Clicking the Esc key or the Save or Cancel button should close and exit the region and return focus to the element that triggered it.
<div> and other container elements are not natively focusable. If
you want to move focus to a container you must set a
for that container. You should also define an
labelledby attribute that identifies the purpose of the container.
If a user action or script updates the content of a page dynamically, you should
aria-live="polite" attribute to the parent element of the region
that changes. Doing so ensures that the contents of the element are read to a
screen reader user, even though the element does not currently have focus. This
method is not intended to be used when the region contains interactive elements.
Content that enhances the experience for one audience might be confusing or
encumber a different audience. For instance, a Close button that looks like
X will be read by a screen reader as the letter X, unless you hide it from
the Accessibility API.
To visibly hide content that should be read by screen readers, edX makes a CSS
class="sr" available to expose content only to non-visual users. This is
achieved by displaying the content beyond the bounds of the viewport, or
clipping the content to a single pixel. These techniques remove any visible
trace of the element from the page, while still leaving it accessible to screen
reader users. This is often referred to as displaying content “offscreen”. In
the following example, a visual user sees only the X, while a screen reader
user hears only “Close”.
<a href="#"> <span aria-hidden="true">X</span> <!-- hidden from screen reader users --> <span class="sr">Close</span> <!-- exposed only to screen reader users --> </a>
The choice to show or hide content for a specific audience should not be taken lightly. Extensive use of offscreen content can reduce accessibility, and is often an indicator of a user experience that relies too heavily on visual context. The following questions should help you decide whether it is appropriate to hide content from screen readers or display it offscreen.
<a href="/" class="inactive">Home</a> <a href="about/" class="active">About Us<span class="sr"> Current page</span></a>
In the code example above, the non-breaking space prevents a screen reader from reading the text as “About UsCurrent Page”.
<label><span class="sr">Type your </span>First Name <input type="text" /> </label>
A minimum contrast ratio between foreground and background colors is critical for users with impaired vision. You can check color contrast ratios using any number of tools available free online.
The only way to determine if your feature is fully accessible is to manually test it using assistive technology; however, there are a number of automated tools you can use to perform an assessment yourself. Automated tools might report false positives and might not catch every possible error, but they are a quick and easy way to detect the most common mistakes.
These are some automated tools for accessibility testing.
By default, the Mac OSX operating system is configured to move keyboard focus to Text boxes and lists only. This setting also applies to browsing web pages using Safari or Firefox with a keyboard. To effectively test keyboard accessibility using a Mac, you should configure your computer to focus on All controls. Open System Preferences, and then select Keyboard. On the Shortcuts tab, for Full Keyboard Access select All controls. You can also toggle this setting with Control+F7.
If you are a Chrome user, this behavior is controlled in a browser setting and is enabled by default. However, if you find that you cannot move focus to links while using Chrome you might need to change your browser configuration. Open Settings, then click Show advanced settings. Under Web content, confirm that the Pressing Tab on a web page highlights links, as well as form fields checkbox is selected.
To test your feature using a screen reader, you can use the following options.