[html4all] Requirement to designate role for embedded content

[Robert J Burns]

Requirement to designate role for embedded content. To ease the burden  
on authoring tools and authors, and to provide further information for  
UAs and users unable to consume non-text media provide an attribute  
and HTML specified attribute NCNames for designating the role of non- 
text media.

<http://esw.w3.org/topic/HTML/EmbeddedContentRoleAndEquivalents>