`<anchorkey>`

The <anchorkey> element allows an author to define a @conref target that will be resolved dynamically when rendered for an end user of the content. This element is useful when doing an initial process of the DITA content prior to final rendering of the content; it allows specified keys to be preserved after that process, and conref relationships which use that key will not be resolved during that initial process.

When a @keyref attribute is specified on an <anchorkey> element, it indicates that any conref relationships using that key will not be resolved. Applications that support run-time resolution of @conref with keys will then be able to dynamically resolve this @conref at display time.

There is no difference between specifying <anchorkey> within a map (in <topicmeta>) and specifying <anchorkey> within a topic. In both cases, processors are instructed to delay resolution of that key for the current set of information. However, the best practice is to only use <anchorkey> within a map. If it is specified in a topic, that topic will define a usage for the key for every user of that topic. This makes the topic less portable, because users that do not want to delay resolution of that specific key will not be able to include the topic in their information.

Many publishing systems for which DITA is used as a source format do not have a way to dynamically resolve content references; those systems will not see any benefit from this element. When DITA is used for those systems, behaviors related to this element are ignored.

Content models

See appendix for information about this element in OASIS document type shells.

Inheritance

+ topic/keyword delay-d/anchorkey

Example

In this example, a set of information contains multiple components. Some references to component A use keys rather than a direct reference, so that @conref can be redirected to a different component when component A is not installed. The keys might be exported, in addition to the IDs, so that some references become bound to the actual component while other references might be redirected.

<map>
  <topicref keys="componentAconfig commonconfig" 
            href="componentA/configA.dita#configA">
    <topicmeta>
      <exportanchors>
        <anchorkey keyref="commonconfig"/>
        <anchorid id="step1"/>
        <anchorid id="step2"/>
      </exportanchors>
    </topicmeta>
  </topicref>
</map>

The @keys attributes declares two distinct keys that can be used to refer to this topic (componentAconfig and commonconfig). Only the second is preserved using <anchorkey>. A task topic from another component might reuse steps within this topic in a variety of ways.

<steps>
  <step conkeyref="componentAconfig/step1"><cmd/></step>
  <step conkeyref="componentAconfig/step1.5"><cmd/></step>
  <step conkeyref="commonconfig/step2"><cmd/></step>
  <step conkeyref="commonconfig/step2.5"><cmd/></step>
  <step><cmd>And that is the end of that</cmd></step>
</steps>

The componentAconfig key is not preserved, so the first <step> becomes <step conref="componentA/configA.dita#configA/step1"><cmd/></step>. At that point the <anchorid> element instructs the step1 ID to be preserved; for runtime applications which support it, this relationship will be preserved in the processed DITA output.
The second <step> with the same key becomes <step conref="componentA/configA.dita#configA/step1.5"><cmd/></step>. However, conref relationships to step1.5 are not preserved, so this conref should be resolved into static content.
For <step> three, the map instructs that both the key commonconfig and the ID step2 should be preserved in any content generated for this DITA topic. For formats that support runtime resolution through keys, a process must convert the @conkeyref value into an equivalent value for that format.
Although resolution for the key used in <step> four is delayed, the specific element that is referenced should not be delayed. Thus the fourth step becomes <step conref="componentA/configA.dita#configA/step2.5"><cmd/></step>. This value is then processed as an ordinary @conref value.

This allows the information assembler to resolve references that must be to componentA while deferring references that can be fulfilled by alternative component content.

Note: This example demonstrates why the <anchorid> element cannot reference an element with the usual topicid/elementid format. If the two <anchorid> elements in the example had been set to config/step1 and config/step2, then they would only ever apply in a topic with id="config". It would not be possible to redirect the key to another topic, but still preserve conref behaviors as desired.

Note: Although it is not specifically called out in this example, it is possible to delay @conref resolution for an entire topic using the key. If @conkeyref on a task topic element is set to "componentAconfig", which is not delayed, the @conref will be evaluated as usual. However, if @conkeyref on the task is set to "commonconfig", which is delayed, resolution of @conref on that element should be delayed by a processor.

Attributes

The following attributes are available on this element: Universal attribute group, outputclass, and the attribute defined below.

@keyref (REQUIRED): Defines a key that, when possible, is preserved in content generated from the DITA source material. Conref relationships that use this key are not resolved when generating that material, so that @conref might be resolved at run-time when an end user is reading the content.