Flicker Rate

Why is this provision necessary?

This provision is necessary because some individuals with photosensitive epilepsy can have a seizure triggered by displays that flicker, flash, or blink, particularly if the flash has a high intensity and is within certain frequency ranges. The 2 Hz limit was chosen to be consistent with proposed revisions to the ADA Accessibility Guidelines which, in turn, are being harmonized with the International Code Council (ICC)/ANSI A117 standard, "Accessible and Usable Buildings and Facilities", ICC/ANSI A117.1-1998 which references a 2 Hz limit. An upper limit was identified at 55 Hz.

How can flashing or flickering elements be identified?

Flashing or flickering elements are usually added through technologies such as animated gif's, Java applets, or third-party plug-ins or applications. Java applets and third party plug-ins can be identified by the presence of APPLET or OBJECT tags. Animated gif's are images that download in a single file (like ordinary image files), but have content that changes over short periods of time. Like other images, however, they are usually incorporated through the use of the IMG tag.

Frames

Why is this provision necessary?

Frames provide a means of visually dividing the computer screen into distinct areas that can be separately rewritten. Unfortunately, frames can also present difficulties for users with disabilities when those frames are not easily identifiable to assistive technology. For instance, a popular use of frames is to create "navigational bars" in a fixed position on the screen and have the content of the web site retrievable by activating one of those navigational buttons. The new content is displayed another area of the screen. Because the navigational bar doesn't change, it provides a stable "frame-of-reference" for users and makes navigation much easier. However, users with disabilities may become lost if the differences between the two frames are not clearly established.
What is the best method for identifying frames?

The most obvious way to accomplish this requirement is to include text within the body of each frame that clearly identifies the frame. For instance, in the case of the navigation bar, a web developer should consider putting words such as "Navigational Links" at the beginning of the contents of the frame to let all users know that the frame depicts navigational links. Providing titles like this at the top of the contents of each frame will satisfy these requirements. An additional measure that should be considered by agencies is to include meaningful text in the frame tag's "title" attribute. Although not currently supported by major manufacturers of assistive technology, the "title" attribute is part of the HTML 4.0 specification and was intended to let web developers include a description of the frame as a quote-enclosed string. Demonstrating the use of the "title" attribute requires a basic understanding of how frames are constructed. When frames are used in a web page, the first page that is loaded must include a frameset tag that encloses the basic layout of the frames on the page. Within the frameset tag, frame tags specify the name, initial contents, and appearance of each separate frame. Thus, the following example uses the "title" attribute to label one frame "Navigational Links Frame" and the second frame "Contents Frame."

client-side image maps

Why do client-side image maps provide better accessibility?

Unlike server-side image maps, the client-side image map allow an author to assign text to each image map “hot spots.” This feature means that someone using a screen reader can easily identify and activate regions of the map. An explanation of how these image maps are constructed will help clarify this issue.

Creating a basic client-side image map requires several steps:

* Identify an image for the map. First, an image must be used in a client-side image map. This image is identified using the img tag. To identify it as a map, use the "usemap" attribute.
* Use the MAP tag to "areas" within the map . The MAP tag is a container tag that includes various tags that are used to identify specific portions of the image.
* Use AREA tags to identify map regions . To identify regions within a map, simply use AREA tags within the MAP container tags. Making this client-side image map accessible is considerably easier to describe: simply include the "ALT" attribute and area description inside each AREA tag.

server-side image map

How do "image maps" work?

An "image map" is a picture (often an actual map) on a web page that provides different "links" to other web pages, depending on where a user clicks on the image. There are two basic types of image maps: "client-side image maps" and "server-side image maps." With client-side image
maps, each "active region" in a picture can be assigned its own "link" (called a URL or "Uniform Resource Locator") that specifies what web page to retrieve when a portion of the picture is selected. HTML allows each active region to have its own alternative text, just like a picture can
have alternative text (see §1194.22(a)). By contrast, clicking on a location of a server-side image map only specifies the coordinates within the image when the mouse was depressed. The ultimate selection of the link or URL must be deciphered by the computer serving the web page.
Why is this provision necessary?

When a web page uses a server-side image map to present the user with a selection of options, browsers cannot indicate to the user the URL that will be followed when a region of the map is activated. Therefore, the redundant text link is necessary to provide access to the page for anyone not able to see or accurately click on the map.

Internet

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color

Why is this provision necessary?

Web page with a green button labled "start" with text above: "Press Green button to Start." There is text above an adjacent red button labeled "cancel" that states "Press Red button to Cancel."

When colors are used as the sole method for identifying screen elements or controls, persons who are color blind as well as those people who are blind or have low vision may find the web page unusable.

Does this mean that all pages have to be displayed in black and white?

No, this provision does not prohibit the use of color to enhance identification of important features. It does, however, require that some other method of identification, such as text labels, must be combined with the use of color. This provision addresses not only the problem of using color to indicate emphasized text, but also the use of color to indicate an action. For example, a web page that directs a user to "press the green button to start" should also identify the green button in some other fashion than simply by color.

Is there any way a page can be quickly checked to ensure compliance with this provision?

There are two simple ways of testing a web page to determine if this requirement is being met: by either viewing the page on a black and white monitor, or by printing it out on a black and white printer. Both methods will quickly show if the removal of color affects the usability of the page.

Multimedia Presentation

What are considered equivalent alternatives?

Captioning for the audio portion and audio description of visual information of multimedia presentations are considered equivalent alternatives. This provision requires that when an audio portion of a multimedia production is captioned, as required in provision (a), the captioning must be synchronized with the audio. Synchronized captioning would be required so someone reading the captions could also watch the speaker and associate relevant body language with the speech.

If a website offers audio files with no video, do they have to be captioned?

No, because it is not multimedia. However, since audio is a non-text element, a text equivalent, such as a transcript, must be available. Similarly, a (silent) web slide show presentation does not need to have an audio description accompanying it, but does require text alternatives to be associated with the graphics.

If a Federal agency official delivers a live audio and video webcast speech, does it need to be captioned?

Yes, this would qualify as a multimedia presentation and would require the speech to be captioned.