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DRAFT: Accessibility Supported Uses for Microsoft Silverlight 2.0

October, 2008

Summary

This document describes initial test results for Accessibility Supported Uses of Microsoft Silverlight 2.0. These results are not complete and this document is a draft. It has been provided to the WCAG working group as an example of how a vendor might document the AT support of a new technology, as part of the WCAG 2.0 implementation package. This document also lists the titles of several techniques that could be used to provide accessible content with Silverlight 2.0.

Design goals around Accessibility support:

Silverlight 2.0 was designed to provide accessibility support using the User Interface Automation API. This API is available natively on Windows Vista, and can be installed on earlier versions of Windows as part of .Net Framework 3.5. Bridges are available to Microsoft Active Accessibility (MSAA), which is an earlier Windows Accessibility API, and to Linux ATK. AT supporting those APIs should work with Silverlight.

Testing Methodology

Testing was done against an interactive application designed to exercise functionality that is difficult to make accessible in HTML and to demonstrate Level A and AA WCAG 2.0 requirements. A separate application was built to demonstrate Multimedia equivalents including captions, audio description and American Sign Language translation. Testing was also done against the set of controls that ships with Silverlight 2.0.

During initial development, testing was done using the UIA Verify tool to verify that information was being properly exposed to UIA, and with the Inspect32 tool to verify that information was being passed from UIA to MSAA correctly via the Windows UIA to MSAA Bridge.

Once we were confident that the information was exposed as expected via the APIs, testing was done on Windows Vista and XP with several Microsoft Active Accessibility based AT, and on Windows Vista using its built in accessibility features which rely on UIA. AT tested included: JAWS 9, NVDA, Windows Vista Narrator, Windows Vista Magnifier, and Windows Vista Speech. Testing was also done to ensure that Silverlight applications could be operated from the keyboard without assistive technology. This document lists 4 permutations, as needed for WCAG 2.0 Candidate Recommendation completion.

Summary of Results

Summary of general test results

Information including name, role, value and state was exposed to both UIA and MSAA AT for most controls. It was possible to operate the UI of most controls from the keyboard in every permutation we tested.

 In all the screen-readers we tried, non-focusable text areas and images were not read. It is fairly easy for the Silverlight application developer to work around this by making all text areas focusable and putting them in the tab sequence. Assistive Technology vendors can also eliminate this problem by implementing text-handling features for Silverlight controls as they do for other types of applications. These non-focusable elements are listed as partial support.

Summary of AT Permutation #1

Windows XP with .Net Framework 3.5, JAWS 9, Internet Explorer 7

Usage notes:

• JAWS does not read ActiveX controls by default. In order to enable JAWS to read Silverlight, the following must be added to the FsDomSrv.ini file, and JAWS must be restarted.

  Add this text to the FsDomSrv.ini file:
  [MS Silverlight Embedded in Internet Explorer using OBJECT Tag with type]
  DLLName=SDomNodeMSAA
  ; TagNameMatch | ParamAndValueMatch
  MappingFlags=96
  Param=application/x-silverlight-2
  TagName=OBJECT
  StartString=Silverlight application start
  EndString=Silverlight application end
  ImplementationFlags=7
  InteractionModeFlags=3

• The user must disable the Virtual Cursor by pressing Ins+Z after the page containing the Silverlight application has loaded.

AT Permutation #2

Windows Vista, NVDA, FireFox 2.0

Usage notes:

• The user must enable NVDA Virtual Buffer Pass-through using Ins+Space after the page containing the Silverlight application has loaded.

AT Permutation #3

• Windows Vista Narrator, Internet Explorer 8 Beta 2

AT Permutation #4

• Windows Vista Magnifier, Firefox 2.0
  

Accessibility Supported Use Cases by Success Criteria

WCAG 2.0 Single A Success Criteria

Success Criteria	Technique	Use	Permutation 1: Windows XP*, Internet Explorer 7, JAWS 9	Permutation 2: Windows Vista, Firefox 2.0, NVDA	Permutation 3: Windows Vista, Internet Explorer 8, Windows Narrator	Permutation 4: Windows Vista, Firefox, Windows Magnifier
1.1.1	SL 1 : Image equivalent	<Image Automation Properties .Name= "text equivalent"	Partial	Partial	Partial	n/a
1.3.1	SL2: Grouping Elements	stackpanel	Supported	Supported	Supported	Supported
1.3.1	SL2: Grouping Elements	Grid	Supported	Supported	Supported	Supported
1.3.1	SL2: Grouping Elements	Items Control	Supported	Supported	Supported	Supported
1.3.1	SL3: User Controls	User control dialog	Supported	Supported	Supported	Supported
1.3.2	SL4: XAML Order	Placing elements in XAML order	Supported	Supported	Supported	n/a
1.3.2	SL5: custom reading order	Automation Properties. Name	Supported	Supported	Supported	n/a
2.1.1	SL7: using built in controls	button	Supported	Supported	Supported	Supported
2.1.1	SL7: using built in controls	checkbox	Supported	Supported	Supported	Supported
2.1.1	SL7: using built in controls	Calendar	Partial	Partial	Partial	not supported
2.1.1	SL7: using built in controls	combobox	Partial	Partial	Supported	Supported
2.1.1	SL7: using built in controls	comboboxitem	Partial	Partial	Supported	Supported
2.1.1	SL7: using built in controls	hyperlink Button	Supported	Supported	Supported	Supported
2.1.1	SL7: using built in controls	password box	Supported	Supported	Supported	Partial
2.1.1	SL7: using built in controls	radio button	Supported	Supported	Supported	Supported
2.1.1	SL7: using built in controls	textblock	Partial	Partial	Partial	not supported
2.1.1	SL7: using built in controls	textbox	Supported	Supported	Supported	Supported
2.1.1	SL7: using built in controls	Toggle button	Supported	Supported	Supported	Supported
2.1.1	SL8: inheriting from an existing control	Inheriting keyboard behavior	Supported	Supported	Supported	Supported
2.1.1	SL9: custom controls	AutomationPeer	Supported	Supported	Supported	Supported
2.1.1	SL3: user controls	scoping keyboard behavior to a user control	Supported	Supported	Supported	Supported
2.4.2	SL15: page title in HTML	Html <title>	Supported	Supported	Supported	n/a
2.4.3	SL4: XAML Order	placing elements in order in the XAML	Supported	Supported	Supported	n/a
2.4.3	SL17: tab Navigation	using the tabNavigation attribute	Supported	Supported	Supported	n/a
4.1.2	SL7: using built in controls	button	Supported	Supported	Supported	n/a
4.1.2	SL7: using built in controls	checkbox	Supported	Supported	Supported	n/a
4.1.2	SL7: using built in controls	combobox	partial	Partial	Supported	n/a
4.1.2	SL7: using built in controls	comboboxitem	partial	Partial	Supported	n/a
4.1.2	SL7: using built in controls	hyperlink Button	Supported	Supported	Supported	n/a
4.1.2	SL7: using built in controls	password box	Supported	Supported	Supported	n/a
4.1.2	SL7: using built in controls	radio button	Supported	Supported	Supported	n/a
4.1.2	SL7: using built in controls	textblock	Partial	Partial	Partial	n/a
4.1.2	SL7: using built in controls	textbox	Supported	Supported	Supported	n/a
4.1.2	SL8: Inheriting from an existing control	Inheriting API support	Supported	Supported	Supported	n/a
4.1.2	SL9: custom controls	Using ApplicationPeer	Supported	Supported	Supported	n/a
4.1.2	SL3: User controls	reuse of objects in user controls	Supported	Supported	Supported	n/a

WCAG 2.0 Double A Success Criteria

Most AA success criteria deal with direct accessibility and do not rely on AT support.

Success Criteria	Technique	Use	Permutation 1: Windows XP*, Internet Explorer 7, JAWS 9	Permutation 2: Windows Vista, Firefox 2.0, NVDA	Permutation 3: Windows Vista, Internet Explorer 8, Windows Narrator	Permutation 4: Windows Vista, Firefox, Windows Magnifier
3.1.2	SL26: language attribute

*UIA support on Windows XP requires .Net Framework 3.5, which can be downloaded for free from Microsoft at the following URL: Download details- .NET Framework 3.5.

Silverlight Techniques and Accessibility Support

Level A Success Criteria

1.1.1 Text Equivalents

• Technique SL1: Providing a name for an image using

  <Image AutomationProperties.Name="text equivalent">

  SL USE: 1 <Image AutomationProperties.Name="text equivalent">

  Image alternatives are exposed to MSAA and UIA. Currently, the AT we tested can only interact with focusable elements in Silverlight.

1.2.1 Audio Video Only

• G158 and G159

1.2.2 Captioning (pre-recorded)

• G158 and G159

1.2.3 Audio Description

• SM8 (New SMIL technique): using Timed Text to synchronize audio description

1.3.1 Info and Relationships

• Technique SL 2: Using Grids, Stack Panels and other grouping elements to group related UI elements

• Technique SL3: Using User Controls to create composite controls of related UI elements

  Example 1: Creating a Dialog with a user control.

1.3.2 Meaningful Sequence

• Technique SL4: Placing XAML elements in the desired reading order

• Technique SL5: Defining custom reading order in custom controls

1.3.3 Sensory Characteristics

• See general techniques

1.4.1 Use of color

• See general techniques

1.4.2 Audio control

• Technique SL6: Using Silverlight Audio Slider

  This is natively supported and does not rely on AT

2.1.1 Keyboard

• Technique SL7: Using built in controls

• Technique SL8: Inheriting from existing controls

• Technique SL9: Adding keyboard support to custom controls

• Technique SL10: Setting focus to the control from javascript in the surrounding page for Firefox

2.1.2 Keyboard Trap

• See general techniques. SL doesn’t cause keyboard traps, but authors could code them.

2.2.1 Timing adjustable

• See general techniques

2.2.2 Pause, Stop, Hide

• G4 and G11

• Technique SL11: Adding a pause button for video playback

  Not AT dependent, as long as it is used in conjunction with one of the SL techniques for 4.1.2, exposing the button to AT

• Technique SL12: Adding a pause button for animation

  Not AT dependent, as long as it is used in conjunction with one of the SL techniques for 4.1.2, exposing the button to AT

2.3.1 3 Flashes or less

• General techniques

2.4.1 Bypass blocks

• Technique SL13: Creating in-page links

• Technique SL14: Placing main content first in reading order

2.4.2 Page Titled

• Technique SL15: Using HTML title in the surrounding page

2.4.3 Focus Order

• Technique SL4: Placing XAML elements in the desired focus order

• Technique SL16: Setting focus order using tabIndex

• Technique SL17: Setting focus order using tabNavigation

2.4.4 Link Purpose

• See general techniques

3.1.1 Language of Page

• Technique SL18: Using HTML of the surrounding page to set language

3.2.1 On focus

• Technique SL19: Avoiding triggering behavior from focus handlers

  This technique will list events to avoid

3.2.2 On input

• Technique SL20: Avoiding triggering behavior from control value changes

  This technique will list events to avoid

3.3.1 Error id

• See general techniques

3.3.2 Labels or instructions

• See general techniques

4.1.1 Parsing

• Technique SL21: Using XAML

4.1.2 Name, Role, Value

• Technique SL7: Using Silverlight built in controls

• Technique SL8: Inheriting from existing controls

• Technique SL9: Implementing an automation peer (UIA interface) in custom controls

• Technique SL3: Using user controls

Level AA Success Criteria

1.2.4 Captions Live

• Same as captions pre recorded

1.2.5 Audio Description

• Same as level A

1.4.3 Contrast ratio

• Technique SL22: Specifying colors

  This is a direct accessibility technique which does not rely upon AT

• Technique SL23: Providing a high-contrast option with a style switching mechanism

  This is a direct accessibility technique which does not rely upon AT. Controls used for switching would need to use SL3, SL7, SL8, or SL9

1.4.4 Resize text

• Technique SL24: Providing a style switching mechanism to resize text

  This is a direct accessibility technique which does not rely upon AT. Controls used for switching would need to use SL3, SL7, SL8, or SL9

1.4.5 Images of text

• Technique SL25: Using advanced text formatting features on real text

  Silverlight has nice, anti-aliased text and many layout and formatting features for it. There should rarely be a need to use an image of text.

2.4.5 Multiple ways

• See general techniques

2.4.6 Headings and labels

• See general techniques

2.4.7 Focus visible

• G149, Future General technique Using the default system focus indicator

3.1.2 Languages of parts

• Technique SL26: Using the language attribute

3.2.3 Consistent navigation

• Technique SL27: Preserving navigational elements when content areas change

  This technique does not require AT support, although the controls used in the navigational elements would need to use other SL techniques in order to support AT

• Technique SL28: re-using user interface components with User Controls

  This technique does not require AT support, but the user controls would need to follow SL8

3.2.4 Consistent identification

• Technique SL28: Re-using user interface components with User Controls

3.2.5 Change on request

• See general techniques

3.2.6 Error suggestion

• See general techniques

3.2.7 Error prevention

• See general techniques

Document Information

Content last updated: 2 November 2008

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