Using Language/Culture Properties as Exposed by Silverlight Applications and Assistive Technologies

Important Information about Techniques

See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.1 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.1.

Applicability

Note

Microsoft has stopped updating and distributing Silverlight, and authors are encouraged to use HTML for accessible web content.

This technique relates to Success Criterion 3.1.2: Language of Parts (Advisory).

Description

The objective of this technique is to use the combination of HTML Lang attribute, CultureInfo and Language to correctly specify the language of the entirety of Silverlight content, or of parts within the Silverlight content.

In general, Silverlight does not attempt to repurpose HTML Lang, because Silverlight is not HTML. Instead, internally within the Silverlight content area, Silverlight uses language definition concepts that relate to XML (Language is a remapping of xml:lang) or .NET Framework programming (CultureInfo). For these reasons, HTML Lang techniques as described in [H58: Using language attributes to identify changes in the human language ] are not useful for Silverlight programming of Silverlight-specific "parts".

What becomes important in Silverlight application programming then is to make sure that the HTML language concept of Lang and the Silverlight language concept of CultureInfo or Lang are not at odds with one another, or reporting misinformation. In particular, application authors should avoid situations where an assistive technology has HTML Lang available for programmatic determination of either page or part, but the effective runtime language in the Silverlight part is different. The result here might be that a screen reader that changes functionality such as phonetic pronunciations would not correctly read the text content from the Silverlight content. Avoiding this situation is largely a matter of due diligence on the part of a Silverlight application author, OR on the part of the Web page author who authors surrounding HTML, in cases where a Web page is embedding Silverlight content or packages that the Web page's author did not actively develop and is only consuming/embedding.

The following is a general recommendation that summarizes the detailed discussion in subsequent subheadings:

HTML Lang

When Silverlight is embedded in an HTML document with the <object> element, the value of the HTML Lang attribute of the surrounding HTML becomes a factor. Browsers process the outer HTML, and the browser's processing has possible influence over values reported to any DOM script that acts, or to any accessibility framework that is reporting the browser content. The preferred way for a Silverlight application to address SC 3.1.1 is to correctly specify the HTML Lang value in the hosting HTML page. This technique should be used in conjunction with H57: Using the language attribute on the HTML element. By using the same language values with both techniques as a better practice, H57 will satisfy 3.1.1 while setting the language value of the Silverlight content to match will assist authors in meeting SC 3.1.2.

The Silverlight runtime itself does not attempt to inherit language settings that come from markup that is outside the Silverlight-specific content. In particular, the HTML Lang attribute applied to the html tag, Lang on host object tag, specific parameters of the Silverlight object tag, all have no affect on the value of any Silverlight Language attribute. Instead, the Silverlight Language defaults to the CultureInfo of the Silverlight runtime as instantiated by HTML object tag invocation. It is expected that if a Silverlight application contains extensive text where language of text is a factor for assistive technology purposes, developers will manually set the HTML Lang tag to match the Language value on the Silverlight root element in XAML. Development tools might or might not enforce or inform the relationship between HTML Lang and Silverlight Language; that consideration is outside the scope of Silverlight as a technology. If language is not a major factor in the application, application authors should consider leaving HTML Lang blank on the hosting HTML page.

You can programatically determine the value of HTML Lang of surrounding HTML from within the Silverlight API, by using the DOM-bridging method HtmlElement.GetAttribute. Otherwise, this can be determined by techniques other than Silverlight's (such as scripting to the HTML DOM of the hosting browser).

Silverlight Language property

Language is an attribute that is available on all Silverlight objects that directly represent a UI element. Language can be queried (or set) by Silverlight managed code run time, such that the Language value can be programatically determined within the Silverlight programming model.

The format of the value that is used to set Language is based on ISO-639-1, and is thus compatible with http://www.rfc-editor.org/rfc/bcp/bcp47.txt.

Language has a behavior that parallels the behavior of xml:lang in an XML document: if Language is set on a parent element, all child elements inherit that Language value. An actual xml:lang attribute in XAML is also valid for this purpose.

Language can be set at the root of a XAML document, so that the entire UI shares the same language setting. If Language is not explicitly set at the root by application markup, Language is inferred per running instance, based on processing the acting CultureInfo at run time.

However, another usage is for application authors to set Language on a specific child element, to override the root-level or client-environment-inferred Language value. This enables consciously embedding a content part that is deliberately in a different language than the remainder of the Silverlight content.

Exactly what happens when a Language is set on a part is not always specified, and is largely a matter of implementation detail of the individual Silverlight classes that might be a "part". However, as an informative generalization, the value of Language might affect considerations such as: how white space is processed (in particular CR or LF); character sets for fonts; string formatting when using APIs specifically on that part.

CultureInfo

CultureInfo is a concept that is relevant to .NET Framework programming. This concept applies to Silverlight because Silverlight uses a specific implementation of a CLR runtime that uses .NET Framework principles. CultureInfo potentially specifies both a language and a culture. This distinction becomes relevant for advanced string formatting concepts that are provided in the .NET Framework, such as decimal separators, dates, and currency. For example, an application author might simply specify "en" if the author did not care about string formatting, but might specify "en-GB" if the application was using string formatting for currency values with the intention of displaying Pounds Sterling as currency unit in string formatting.

Silverlight applications often run using an inferred CultureInfo based on the operating system where the user agent browser host exists (in other words, the culture of the client computer where the Silverlight application is run). This CultureInfo can be queried by applications at run time; see CultureInfo.CurrentCulture. Application authors can deliberately constrain the set of CultureInfo cases that a Silverlight application can be run under, in order to verify that necessary string resources for that culture are available in that application. This is done by setting <SupportedCultures> in the Silverlight project settings. If a user accesses the application on a client that is outside the SupportedCultures, the application author has the following choices:

  • Use a fallback resource set representing a neutral culture; this is enabled automatically by the Silverlight resources lookup behavior, so long as the project includes resources identified as being culture-neutral. This is the preferred approach.
  • Use client logic to detect the culture, and initiate a client-side redirect to request either a different XAP or a different hosting HTML page.
  • Trap requests at the server level by checking lang request in the header. This varies between server implementations, is not a Silverlight-specific technique, and is not discussed here.

For more information, see How to: Create a Build that Targets a Specific Culture.

CultureInfo generally applies to the Silverlight application as a whole. There are advanced techniques whereby worker threads can be run as separate cultures, but that is not discussed here and is not relevant because only the main UI thread has relevance to Web content accessibility. So, if an application author wants to declare specific language settings for a part (component, region or control) of the Silverlight application, a different Silverlight-specific property Language is used.

Examples

These examples show Silverlight behaviors that are based on interpreting the Language property value, as a way of illustrating the programmatic determination of language values specifically in the Silverlight application framework. To determine HTML Lang, application authors should use the HTML DOM as enabled by browser host scripting, rather than Silverlight APIs. HTML DOM techniques are not shown here because they are specific to browsers or scripting frameworks, not to Silverlight.

Example 1: Language set at root-level of Silverlight content, inherits

This example features a XAML UI and logic that reports information to demonstrate that the information is programmatically determinable. This example shows determination of the Language property. 

<UserControl x:Class="LangProperties.MainPage" 
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   Language="en-gb">
 <StackPanel x:Name="LayoutRoot" Background="White">
       <Border BorderBrush="Red" BorderThickness="2">
           <TextBlock Language="zh-cn" Text="（（）共" Name="t2" VerticalAlignment="Top" TextWrapping="Wrap" Height="100"/>
       </Border>
       <Border BorderBrush="Red" BorderThickness="2">
           <TextBlock Text="（（）共" Name="t3" VerticalAlignment="Top" TextWrapping="Wrap" Height="100"/>
       </Border>
       <Button Click="button1_Click">IETF Language of this app</Button>
 </StackPanel>
</UserControl

private void button1_Click(object sender, RoutedEventArgs e)
{
   Button b = sender as Button;
   MessageBox.Show(b.Language.IetfLanguageTag);
   // this will be 'en-gb' because inherits from the root
}

This example is shown in operation in the working example of Language Properties.

Example 2: Determine CurrentCulture; runtime verification that CurrentCulture and the surrounding HTML's current Lang value do not report different language settings

The following is an event handler that can be hooked to an object lifetime event such as UserControl.Loaded on the Silverlight XAML root. This example demonstrates property access to several of the relevant language properties that are present in Silverlight and shows a specific way to compare CultureInfo and Lang by a "not equals" check after constructing a CultureInfo based on the Lang string. To apply this test, the hosting HTML page may need to be altered to declare a specific HTML Lang; default Silverlight aspx or html test pages do not declare HTML Lang. 

       private void RunLanguageDetectLogic(object sender, RoutedEventArgs e)
       {
           CultureInfo thisAppCC = CultureInfo.CurrentCulture;
           CultureInfo thisAppCUIC = CultureInfo.CurrentUICulture;
           HtmlDocument thisPage = HtmlPage.Document;
           String thisAppHTMLLang = (string) thisPage.DocumentElement.GetProperty("lang");
           CultureInfo CCFromLang = new CultureInfo(thisAppHTMLLang);
           if (CCFromLang != thisAppCC && CCFromLang.ToString() !=  "")
           {
               TextBlock tb = new TextBlock();
               tb.Text += "Warning: the current culture for the run time (";
               tb.Text += thisAppCC.ToString();
               tb.Text += ") does not match the culture indicated in hosting HTML's Lang (";
               tb.Text += CCFromLang.ToString();
               tb.Text += ").";
               tb.Inlines.Add(new LineBreak());
               tb.Inlines.Add("Typical action here would be to redirect the request to an HTML page
                 where the Lang is correct for user's current culture as determined from the OS.");
               LayoutRoot.Children.Add(tb); 
               //LayoutRoot refers to the default MainPage.xaml element from a VS-template Silverlight Application
           }
       }

Resources

Resources are for information purposes only, no endorsement implied.

Tests

Procedure

  1. Using a browser that supports Silverlight, open an HTML page that references a Silverlight application through an object tag.
  2. Verify that language settings are respected by individual Silverlight control characteristics. (Exactly what behavior manifests the language difference varies per Silverlight class implementation. For some testing ideas, see Creating Globally Aware Applications).
  3. Verify that any interaction between HTML Lang in the HTML and the Language or CultureInfo from the Silverlight application do not result in a clash of language information, either in terms of basic application behavior or in how an assistive technology decides to process language information.

Expected Results

#2 and #3 are true.