@rel cleanup in multiple locations

@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 [1]. No mappings to assistive technology have been created for the individual values of @rel [1]. 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 [2]. 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:

1. Governance of the terms and definitions.
2. Mappings to AT and/or default ARIA semantics?
3. Clarification of effect of @rel on RDFa browsers, especially schema.org processors.

[1] https://www.w3.org/TR/html51/semantics.html#linkTypes

[2] https://www.w3.org/TR/html51/semantics.html#other-link-types

[3] http://microformats.org/wiki/existing-rel-values#HTML5_link_type_extensions

[4] http://www.iana.org/assignments/link-relations/link-relations.xhtml

Going to disturb the crickets here for a bit to update these two links:

• https://www.w3.org/TR/html51/links.html#sec-link-types
• https://www.w3.org/TR/html51/links.html#sec-other-link-types

The overall “authority” question (and related governance concerns) around non-URI link relationship values does need addressing.

@mnot has been in lengthy conversations on this front in the past and his input here would be most helpful.

That said, it may be best to break down the issues that need addressing here into related projects/tasks. There’s a good bit in the initial post (governance, accessibility tech mapping, etc).

Lastly, it should certainly be noted that the use of rel values (thanks to the Link header and reuse of the concept/tool in other media types) far exceeds the scope of HTML5 and even “the browser.” For instance, the popular Hypermedia Application Language uses rel values extensively–and it’s among many similar peers in the space which do similar things.

to digging through the issues here and creating some achievable targets / goals.

We’ve got this on the HTML issues list already. We didn’t manage to deal with it for HTML 5.1 (which is pretty much hitting feature freeze) but I’ll bump the priority and try to get it dealt with for early 5.2 drafts…