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Living Examples - Scripting Languages |
(l)When pages utilize scripting languages to display content, or to create interface elements, the information provided by the script will be identified
with functional text that can be read by assistive technology.
Client-side scripting languages are coded in with the page's content and HTML tags, and are executed by the user agent (i.e. web browser). If necessary,
you can check for the presence of a scripting language on a web page by reading through the source code for the <script> tag (e.g. <script src="scriptname.js" language="JavaScript1.2">).
A rollover button script uses graphical images as link buttons. The image changes when the mouse pointer moves over it.
A "pull right" menu script makes use of additional navigation selections that "slide" out from a main navigation selection (e.g. if you placed the mouse
pointer over a menu item that says "Personnel," a new list of menu items reading "Management," "Support Staff," and "Research Team" will appear either
to the side or underneath the "Personnel" selection).
Assistive technology must be able to read and announce the presence of all links within a scripting language-controlled navigation system.
For rollover buttons, ensure that all graphic images contain the alt attribute.
In the event that such a navigation system cannot be accessed by assistive technology (e.g. the event handler triggering the script cannot be activated
through the keyboard), or because the user does not access the page with a mouse (e.g. blind or quadriplegic users), the script will need to be rewritten
to make use of keyboard commands, or an additional navigation mechanism that contains hyperlinks will have to be created.
WARNING: If this additional navigation is placed inside <noscript></noscript> tags, it will not be read by assistive technology when the browser's scripting
capabilities are left on (in such a case, the browser will correctly ignore the <noscript></noscript> tags). The <noscript></noscript> tags should be used
to accommodate those with older browsers or text browsers, but the same exact menu must also be made available somewhere outside of the tags.
NOTE: The majority of assistive technologies can negotiate rollover button navigation mechanisms, but many still have difficulties with "pull right" menus.
In addition to rollover buttons that are apart of a navigation mechanism, scripts can also cause content-bearing graphics that do not come in contact with
mouse movement to appear and be replaced.
As with any graphical image, content contained on a graphic and its <img> tag's alt attribute must be identical. However, although the <img> tag that positions
the original graphic (i.e. the graphic that appears when the page first loads) will contain an alt attribute, the alt content does not change when the
image does. Therefore, all content that is displayed on images must be duplicated somewhere on the page, or be made accessible via a link.
Form validation is the act of ensuring that all information entered into an electronic form is of the correct format, or of ensuring that required fields
have been filled in. Scripting language-controlled form validation is particularly susceptible to assistive technology incompatibility.
Assistive technology must be able to read the content displayed in any form validation alert box, and must allow the user to select the OK button (or any
other buttons that might be present) to clear the alert box and return to the form. The majority of assistive technologies are capable of performing these
tasks.
Another way of passing this checkpoint is to write the form validation script so that the form page refreshes with alerts as to which fields were improperly
filled in or left blank printed on the page itself; assistive technologies will read these alerts as it would any other content.
Because assistive technology cannot ascertain the color or any other style characteristic of screen font, do not instruct users to re-enter or correct entries
marked in red or marked in bold.
A form validation script might automatically move the cursor to a field that was entered incorrectly.
Assistive technology must allow the user to know which field the cursor has been moved to. Generally, assistive technologies provide the user with the ability
to hear the name of the form element in which the cursor currently resides.
It is the developer's responsibility to ensure that the cursor is correctly relocated to the form field that needs correcting.
The form might have a mechanism that allows the user to fill in a numerical value for a particular year, then click a button that automatically
fills subsequent year form fields with the identical value.
Assistive technology must identify the new value to the user. Generally, assistive technologies provide the user with the ability to hear the name of the
form element in which the cursor currently resides. If such an update occurs in fields following the auto-fill mechanism button, the assistive technology
will read the new value when the cursor arrives at that form field.
It is the developer's responsibility to ensure that the correct values are placed inside the form fields.
Several event handlers require a specific kind of input device. Input devices may include pointing devices (such as the mouse), keyboards, braille devices,
head wands, microphones, and others.
An example of a device-dependent script is onDblClick: it requires a mouse, but there is no keyboard equivalent for double clicking, so a user that does
not use a mouse cannot access content or perform a function provided by onDblClick.
Scripting must be device-independent or provide multiple input and output options for different devices.
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Curator:
Responsible NASA Official:
Last Updated: March 6, 2009
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