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XForms Accessibility 编辑

Intoduction

This article provides a quick guide to how accessibility is handled in Gecko for XForms.. Assistive technologies API for XForms is supported starting from Firefox 3 (Gecko 1.9). Implementation of accessible objects for XForms elements is based on top of the existing object hierarchy introduced in the Mozilla accessibility module. XForms elements behavior is implemented in accordance with accessible toolkit checklist.

In general, when elements are similar to HTML elements, they are exposed to MSAA/ATK in a similar way.

Get Build

Subsections below explain how you can obtain accessible XForms-enabled build. These are either downloading latest build of firefox or building it yourself.

Downloading Builds

Notion: XForms is no longer distributed with Firefox build. You must build it yourself. See section below.

For Firefox, you may directly download the nighly "trunk" build of Firefox and install the XForms extension which lives in 'xpi' directory of the build. Note, XForms accessibility is implemented only on trunk. Trunk builds are not considered stable and should not be installed on top of the Firefox used for daily browsing. Currently we have verified that XForms accessibility is working on the Windows platform, and Linux testing has not yet been done, although everything should work and is ready to be tested. You will find trunk builds of Firefox at ftp.mozilla.org, trunk builds of XForms extension (Windows) at ftp.mozilla.org or trunk builds of XForms extension (Linux) ftp.mozilla.org.

Build It Yourself

If you would like to build firefox/seamonkey yourself then please ensure your .mozconfig file has the following option:

ac_add_options --enable-extensions=default,xforms,schema-validation

How To Test

There are two approaches to test XForms accessibility. The first is to use and assistive technology such as a screen reader, or an accessibility testing tool, to make sure XForms elements have proper accessible objects. Or you may be guided by toolkit checklist to check keyboard navigation for XForms controls.

You can try the following link to test XForms accessibility:

visual XForms elements in XHTML document at bugzilla.mozilla.org
visual XForms elements in XUL document at bugzilla.mozilla.org
you can see XForms sample tests at Mozilla XForms project
there are set of tests at beaufour.dk
W3C's XForms test at w3.org

Keyboard Navigation Issues

Navigation Sequence

Though XForms spec declares navindex attribute to define the navigation sequence (see 1.0 specs or 1.1 specs) but Rich Schwerdtfeger (Distinguished Engineer, SWG Accessibility Architect/Strategist Chair, IBM Accessibility Architecture Review Board) gave some clarification about navindex. He wrote:

Navindex was in XForms - it was stripped out as it was believed the focus model was dependent on the content which used it. So, yes we don't care about navindex in XForms. If you use xhtml1.x use tabindex. If you use Xhtml2 use nextfocus.

Therefore since Mozilla XForms works in XHTML (1.x) or XUL documents only then we use tabindex instead. Note, we support -moz-user-focus style neither for XHTML or XUL.

AT API

Accessible properties

This section describes common rules how accessibility properties are formed for forms control elements.

name

It is formed from value of child XForms label element if the element doesn't have labelledby attribute.

description

It is formed from value of child XForms hint element if the element doesn't have describedby attribute.

state

It is formed as well from model item properties (MIPs) of instance node that XForms element is bound to as from valid/invalid or in-range/out-of-range states of instance node. Instance node states are mapped to accessibility state constants declared in nsIAccessibleStates interface like it shown below:

relevant - STATE_UNAVAILABLE
readonly - STATE_READONLY
required - STATE_REQUIRED
invalid - STATE_INVALID
out of range - STATE_INVALID

attributes

Redefines datatype ARIA attribute. Its value is XML Schema builit-in datatype of instance node that XForms element is bound to.

children

Mozilla XForms implementation allows form control elements to have child elements. Therefore accessible children are formed from any accessible child elements of form control element and from elements that are introduced by its presentation.

Forms Controls Module

Some of form control elements may be represented in few ways by different widgets. This section lists accessible presentations for form control elements.

input

A key xforms element to show and change the instance data to which it is bound (see the spec, the docs). The follwoing representations input element are accessible:

text field - see the docs.
checkbox - see the docs
datepicker - see the docs.
calendar - see the docs.
days list - see the docs.
months list - see the docs.

secret

Used for inputting passwords (see the spec, the docs). This element is represented by password field.

textarea

Serves to show/change multiline text (see the spec, the docs). This element is represented by multiline text field.

output

Serves to show instance data that the element is bound to (see the spec, the docs). It can have the following presentations:

text - see the docs.
calendar - see the docs.

upload

Provides a means for the user to select a file (see the spec, the docs). This element is represented by upload.

range

Allows the user to choose a value from within a specific range of values (see the spec, the docs). Currently it is represented by a slider only.

trigger

Allows the user to initiate actions (see the spec, the docs). This element is represented by button.

submit

Invokes the submission of the selected instance data to its target destination (see the spec, the docs). This element is represented by button.

select

Allows the user to choose one or multiple values from a list of pre-defined values (see the spec, the docs). It can have the following representations:

select1

Allows the user to choose a single value from a list of pre-defined values (see the spec, the docs). It can have the following representations:

Additional Elements

These elements may be used as child elements to the form controls described above. Some of these elements are not accessible itself but they makes accessibility properties for XForms elements that hold them.

label

Specifies the label for the xforms control (see the spec, the docs). Every form control other than the output element must contain a label element. The value of label element is used as name of accessible object.

help

Specifies contextual help for the containing form control (see the spec, the docs). The help element has ROLE_ALERT role.

hint

Similar to a tooltip (see the spec, the docs). The value of hint element is used as description of accessible object.

alert

This message will be shown when the form control cannot properly bind to instance data or when the instance data value is invalid or out of the specified range of selectable values (see the spec, the docs). The alert element has ROLE_ALERT role for both usual and inline alert elements.

message

Used in combination with event listeners to display a message to the user when the specified event occurs (see the spec, the docs). The message element has ROLE_ALERT role.