A topic may contain several types of links.
- Content reference links from any element in the topic that allows @conref or @conkeyref.
- Related information links, within a <related-links> element following the topic body. The related links are usually rendered at the end of the topic.
- Image links created using <image>. Image elements may use <longdescref> to link to the long description for the image as a supplement to the <alt> element.
- Object links created using <object>. Object elements may use <longdescref> to link to the long description for the object as a supplement to the <alt> element.
- Navigation links created using <xref>. For output media that support hyperlinking, the <xref> should result in a hyperlink.
- Navigation links created using @keyref on elements that allow @keyref but not @href (e.g., <ph>, <cite>, <keyword>, and <term>).
- Metadata associations using <data-about> in contexts where <data> is allowed.
- Navigation links from long quotes to the source of the quote using <longquoteref>.
Links to resources outside a topic's containing XML document that use direct URI-based addresses establish unconditional topic-to-resource dependencies. Such dependencies can impede reuse in two ways:
- The linking topic cannot be used in a given map unless the dependent resource is also used.
- The linked resource cannot be dynamically changed based on the map context in which the linking topic is used.
These issues can be avoided by using key-based addressing. Because keys are defined in maps, each map that uses the linking topic can bind the key to the most appropriate resource.