While this section of the spec [3.2 Elements & 3.2.1 Semantics] introduces the use of semantics and how they relate to conformance, the examples given dont convey the negative impact incorrect or insufficient semantics can have on the user experience, in particular for users of Assistive Technology. 

I suggest the following or similar spec text be added to the Elements section to illustrate these issues and to provide a deeper sense of context and purpose behind the need to create conformant content. 

This text could go in either 3.2.1 Semantics or in the following section 3.2.2 Elements in the DOM. [1]

Draft Spec text 

<sample spec text>

"At all stages, in a dynamically generated or altered document the semantic integrity of the document snapshot must be maintained at each step in the document mutation  in particular where the document is in a steady state (after a user interaction for example). These rules may be relaxed to some degree during transitional steps involve background transition or operations with other APIs but, if the document is to be a conformant HTML5 doc, then suitable elements/attributes from this spec must be used in a way that supports the documents integrity, the UA parsing requirements and above all the user experience as this can impact on the usability and accessibility of the content. 

Maintaining this integrity will assist user agents such as Assistive Technologies understand and successfully interact with the DOM or other user agent structures, [ref]. This means that a dynamic widget which is semantically structured to be accessible on a page load, will when responding to user interaction/input have to maintain its semantic structure as scripting or other dynamic events are applied and the widget content/structure is altered, in order to be considered conforming html. 

This example is applicable to processes such as a checking out cart, or in mashup type applications and semantic integrity will help to maintain the interoperability of application/document structures as well as facilitate a more consistent user experience. ** 
Examples of where this kind of mutation or dynamically altered content can impact on the user can be found in WCAG." 
</sample spec text>

 Related WCAG SC, Fails etc 
**SC 2.4.5: note wcag reference to dynamic processes [2]
F76: Failure of Success Criterion 3.2.2 due to providing instruction material about the change of context by change of setting in a user interface element at a location that users may bypass(context change in an interface) [3]
G13: Describing what will happen before a change to a form control that causes a change of context to occur is made. [4]


[1] http://www.w3.org/TR/2011/WD-html5-20110525/elements.html#elements
[2] http://www.w3.org/TR/UNDERSTANDING-WCAG20/navigation-mechanisms-mult-loc.html
[3] http://www.w3.org/WAI/GL/WCAG20-TECHS/F76.html
[4] http://www.w3.org/TR/WCAG20-TECHS/G13