structure and types of content can also be specified using role in XHTML 2.0

An example start tag of a root element might look like:

<html xmlns="http://www.w3.org/2002/06/xhtml2" xml:lang="en"
      xmlns:wairole="http://www.w3.org/2005/01/wai-rdf/GUIRoleTaxonomy#" >

Roles can be embedded in any host language, e.g. [XHTML] 1.1. In this example, a table has been assigned the role of a spread sheet.
For example:
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:x2="http://www.w3.org/2002/06/xhtml2" xmlns:wairole="http://www.w3.org/2005/01/wai-rdf/GUIRoleTaxonomy#">
<body>
<table id="table1" x2:role="wairole:spreadsheet" >

...
Encapsulated in the role information is information for the operating system that enables it to be properly treated. (In this case that multiselectable is supported.)

A full list of roles is availible at http://www.w3.org/WAI/PF/Group/GUI/
(will be http://www.w3.org/WAI/PF/GUI/)

We can also make some standard CSS classes wich mimick the roles

Summary of LD web standard CSS classes

Complex: This class is used to indicate that the text is complex. A simplification may be available in the title attribute of the tag.
Clarification: This class is used to indicate that the text is ambiguous. A thesaurus equivalent of how the word is used may be available in the title attribute of the tag.
Glossary: This is a class used for links that take users to a glossary or simple explanation of the linked to term.
NonLiteral: This class is used to alert the user that the following text is not to be taken literally. A clear text explanation may be provided in the title.
Supplemental: This class is used to mark content that the user may not need in a summarized version of the page
Important: This section is highly important to the user. It should be included and emphasized in a summarized version of the page.
Warning: This text is an important warning for the user
Instruction: This section of text tells the user what to do
ExtraHelp: This section of content should normally not be displayed. In a version where more help, such as symbols or pictures are needed, this content should be displayed. To ensure this class is not normally shown, set display to not visible in the default style sheet.

SO you can say
<Div class=warning>
DO not ever use this appliance near water
</div>

The user agent can know to make this class in red with an icon next to it for specific users -without the author creating or changing the look of their page

All the best
Lisa