[ac] (0) Accessibility of <canvas> is not optional. (credit: sf)

git-svn-id: http://svn.whatwg.org/webapps@2868 340c8d12-0b0e-0410-8428-c7bf67bfef74

index

@@ -20089,8 +20089,8 @@ interface <dfn id=cuerangecallback>CueRangeCallback</dfn> {
   elements (typically <code><a href=#the-h1,-h2,-h3,-h4,-h5,-and-h6-elements>h1</a></code>) and then styled using CSS and
   supporting technologies such as XBL.</p>
 
-  <p>When authors use the <code><a href=#the-canvas-element>canvas</a></code> element, they should
-  also provide content that, when presented to the user, conveys
+  <p>When authors use the <code><a href=#the-canvas-element>canvas</a></code> element, they must also
+  provide content that, when presented to the user, conveys
   essentially the same function or purpose as the bitmap canvas. This
   content may be placed as content of the <code><a href=#the-canvas-element>canvas</a></code>
   element. The contents of the <code><a href=#the-canvas-element>canvas</a></code> element, if any,

source

@@ -21785,8 +21785,8 @@ interface <dfn>CueRangeCallback</dfn> {
   elements (typically <code>h1</code>) and then styled using CSS and
   supporting technologies such as XBL.</p>
 
-  <p>When authors use the <code>canvas</code> element, they should
-  also provide content that, when presented to the user, conveys
+  <p>When authors use the <code>canvas</code> element, they must also
+  provide content that, when presented to the user, conveys
   essentially the same function or purpose as the bitmap canvas. This
   content may be placed as content of the <code>canvas</code>
   element. The contents of the <code>canvas</code> element, if any,