In the Using LINK to define document specific toolbars section of The Head Element and Related Elements part of the now expired HTML 3.0 draft Dave Raggett wrote
An important use of the LINK element is to define a toolbar of navigation buttons or an equivalent mechanism such as menu items.
LINK relationship values reserved for toolbars are:
- REL=Home
- The link references a home page or the top of some hierarchy.
- REL=ToC
- The link references a document serving as a table of contents.
- REL=Index
- The link references a document providing an index for the current document.
- REL=Glossary
- The link references a document providing a glossary of terms that pertain to the current document.
- REL=Copyright
- The link references a copyright statement for the current document.
- REL=Up
- When the document forms part of a hierarchy, this link references the immediate parent of the current document.
- REL=Next
- The link references the next document to visit in a guided tour.
- REL=Previous
- The link references the previous document in a guided tour.
- REL=Help
- The link references a document offering help, e.g. describing the wider context and offering further links to relevant documents. This is aimed at reorienting users who have lost their way.
- REL=Bookmark
- Bookmarks are used to provide direct links to key entry points into an extended document. The TITLE attribute may be used to label the bookmark. Several bookmarks may be defined in each document, and provide a means for orienting users in extended documents.