Introduction
Information types and topics
Topics are the building blocks of modular documents, and organising topics by semantic information types is one of the architectural features of DITA.
DITA map files
Syntax and mark-up
Language and punctuation
Graphics and figures
Cross-referencing
Cross-references are a means of binding individual topics into a coherent and navigable document.
- Types of cross-references
  A cross-reference is used in DITA to link or associate one piece of content with another. The cross-reference (xref) element is the primary mechanism for cross-referencing, but other elements also have cross-referencing functions.
- The xref element
  The cross-reference element is used for linking or otherwise cross-referencing text within a topic to other topics, elements within a topic, or resources external to the DITA collection.
- Avoiding in-text cross-references to topics
  Cross-references to other topics should be stored in the relationship table of the ditamap, external to the topic, and not in-line within the text of the topic.
- Cross-referencing topics and external resources
  Cross-references are commonly made to other DITA topics in a collection, and to information resources outside the collection. These external targets can be any type of electronic resource that can be addressed through a URI, including e-mail addresses, documents on a network file server, and Web content.
- Cross-referencing elements in a topic
  Cross-references to elements within topics such as figures and tables allow a reader to easily navigate through a document, whether it is in a page layout format or a hypertext format. The xref element is always used for cross-referencing elements within a topic.
- Links in related-links sections
  When a topic requires cross-references to other topics where those cross-references will always be valid in the context of the topic, they should be contained within a related-links section after the topic body. In all other cases, cross-references should be defined in the relationship table of the ditamap.
- Managing cross-references
  - Cross-referencing a ditamap
    Cross-references to ditamaps should not be used, because DITA does not have a clear method for doing so, and the logic of linking to metadata is not strong.
  - Removing related links from the output
    Related links can be removed from the output by setting the linking attribute of the topicref element in the ditamap to none. If you are producing HTML-based output, you can alternatively change the CSS class definition so that generated links are not displayed.
  - Conditions in cross-references
    The standard DITA metadata attributes of audience, platform, product, and otherprops can be applied to xref elements to allow conditional processing of cross-references. Positioning cross-references at the end of a sentence makes it easier to exclude the cross-reference without affecting the sense of the sentence.
- Cross-references in titles
  You should not use cross-reference elements within topic titles.
Content re-use
Metadata, conditional processing, and indexing
The DITA documentation process
DITA authoring concepts
Moving from style-based authoring to a structured authoring methodology such as DITA requires a radically different approach to writing.

Conditions in cross-references

The standard DITA metadata attributes of audience, platform, product, and otherprops can be applied to xref elements to allow conditional processing of cross-references. Positioning cross-references at the end of a sentence makes it easier to exclude the cross-reference without affecting the sense of the sentence.

If you need to cross-reference different resources for different publication variants, use the audience attribute to define these conditions. For example, if the PDF version of the output links to a different resource than the Help version, you could include two adjacent xref elements, one with the audience attribute set to pdf_user, and the other set to help_user.

For DITA 1.2 and above, the keyref mechanism should be used in preference to duplicating and conditionalising elements.

If you are using cross-references in conjunction with conditional processing, positioning an in-text cross-reference (xref) element at the end of a sentence makes it easier to exclude.

For example, if a cross-reference is to be included in the Web rendition of a DITA collection, but excluded from the PDF rendition, then audience attribute might be used to differentiate the PDF-only text.

The code:

<p>The coolant expansion tank is attached to 
the firewall<ph audience="help_user">, as shown in 
<xref href="c_engine_bay#eng_bay/fig_coolant_system" type="fig"/></ph>.
</p>

might be rendered in the output as The coolant expansion tank is attached to the firewall. when the help_user content is excluded, and as The coolant expansion tank is attached to the firewall, as shown in Figure 3. otherwise.