@rel could be extremely powerful, but there is hesitancy to implement because of unpredictable behavior. What makes
@rel so complicated?
The HTML spec has a short list of allowed values for @rel . No mappings to assistive technology have been created for the individual values of @rel . Some of these (e.g. “prefetch”) might not have significant effect on AT or AT users, but others (e.g. “bookmark”) could benefit AT users tremendously. This attribute generates triples in some circumstances. As developers without great knowledge of RDFa increase their use of vocabularies such as schema.org, it is necessary to clarify the effect of @rel (and @rev) on RDFa browsers or, at a minimum, schema.org processors.
In an admirable attempt to make @rel extensible for everyone, anyone can add a value for @rel . The result is that @rel is underspecified. Values for @rel are listed in 3 places (cf [3. 4]), and many of the definitions are not clear. Removed terms (e.g. “index”) remain in the Microformats table with no clear flag. There is no consistency in naming. The microformats list includes hyphens, underscores, and periods in lieu of spaces and/or namespaces. It is time to define parameters for @rel wrt to accessibility and RDFa processing. There seem to be 3 distinct problems:
- Governance of the terms and definitions.
- Mappings to AT and/or default ARIA semantics?
- Clarification of effect of @rel on RDFa browsers, especially schema.org processors.