Fontdef References a downloadable font definition file. Glossary References a document providing a glossary of terms that pertain to the current document. Help 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. Home References a home page or the top of some hierarchy.
Index References a document providing an index for the current document.
Next References the next document to visit in a document structure or guided tour. Previous References the previous document in a document structure or guided tour. ToC References a document serving as a table of contents. If the document is part of a hierarchy, this references the immediate parent of the current document. The LINK element can be used to define a toolbar of navigation buttons or an equivalent mechanism such as menu items.