As described in HTML4 Meta data profiles and XHTML Meta Data Profile (XMDP) description:
HTML4 definition of the 'rel' attribute. Here is an additional value as defined in the rel-tag specification.
HTML4 definition of the 'class' attribute. This meta data profile defines some 'class' attribute values (class names) and their meanings as suggested by a draft of "Hypertext Links in HTML". All values are defined according to the semantics defined in the hAtom specification.
The 'value-title' class name has been incorporated from the value-class-pattern for improved accessibility, internationalization, and localization.
The 'category' property has been incorporated in order to provide more flexible tagging than just depending on rel-tag.
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