When the <anchorid> element is defined within a topic prolog, the specified IDs will be found within that topic. When an <anchorid> element is defined within a <topicref> element, the specified IDs will be found within the referenced topic (if the <topicref> references a collection of topics, such as a reference that uses only a file name, the IDs will be found within the first or root topic).
The only difference between specifying an <anchorid> in the
<prolog> and specifying it in the
<topicmeta> is that from the map it is possible to export the ID of
the entire referenced topic. If
<anchorid id="zero"/> is specified in
the <topicmeta>, and the referenced topic has an id of "zero", this
means that the <anchorid> is a reference to the entire topic. If the
topic id is not "zero", then the <anchorid> is a reference to the
element with id="zero" within that topic.
Along with the preservation of the element's ID, any @conref attribute that references the element's ID will not be resolved during an initial process. In that case, the @conref will be resolved during a later rendering process.
This description does not imply that IDs are not discarded when <anchorid> is not used; though this element requires that IDs be preserved in some manner, it is also common for IDs to be preserved when <anchorid> is not used. Thus the primary impact of the <anchorid> element is on @conref resolution.
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.
Why not use topicid/elementid?
This element differs from normal DITA referencing syntax in that it can reference an element within a topic without using the topic's ID. There are two reasons for this. First, the <anchorid> element might only be defined in a situation that refers unambiguously to a single topic (in the <prolog>, or in the <topicmeta> for a reference to a topic). Second, it allows the <anchorid> to be combined with key values.
It is possible to combine an <anchorid> with a key in order to delay resolution of @conref in the topic represented by that key (see the second set of examples below). This would not be possible if the <anchorid> element required both the topic id and the element id. That is, @keyref allows a modifiable reference to a topic, so a map might instruct processors to delay conref for item "step1" in the topic represented by the key "commonconfig". If the <anchorid> element required a topic id, the delayed conref would always be bound to that specific topic.
See appendix for information about this element in OASIS document type shells.
+ topic/keyword delay-d/anchorid
Use case 1: Runtime resolution of @conref to an id, determined by original author
- Author 1 creates topics for information component A, which is a common component used
by many products. The configuration task for component A is often reused in whole
part, so the author assigns ids to each of the steps in the procedure and exports
<task id="configA"> <title>ABC</title> <shortdesc>...</shortdesc> <prolog><metadata> <exportanchors> <anchorid id="step1"/> <anchorid id="step2"/> <anchorid id="step3"/> </exportanchors> </metadata></prolog> <taskbody> <steps> <step id="step1"><cmd>Do this</cmd></step> <step id="step2"><cmd>Do the other</cmd></step> <step id="step3"><cmd>And then finish</cmd></step> </steps> </taskbody> </task>
- Author 2 is working on information component B, which has information component A as a prerequisite.
- Author 2 creates a configuration task that reuses two steps from the configuration
task in information component
<task id="configB"> <title>..</title> <shortdesc>..</shortdesc> <taskbody> <steps> <step><cmd>Do the very first thing</cmd></step> <step conref="componentA/configA.dita#configA/step1"><cmd/></step> <step><cmd>Do the middle thing</cmd></step> <step conref="componentA/configA.dita#configA/step2"><cmd/></step> </steps> </taskbody> </task>
- Author 2 builds the content for component B into a deliverable format that supports dynamic content resolution. As with traditional conref, the source for component A must be available during this process. Because the ids in configA are exported, the build process knows to preserve the reuse relationship rather than resolve it - so the @conref reference to the steps becomes an equivalent reuse artifact in that deliverable format. This way the relationship to component A can be resolved at runtime, and pick up the user's version of component A, which might be more up-to-date than the one used by Author 2 when component B was built.
Use case 2: Runtime resolution to an id exported by the information builder
- Author 1 is creating content that will be packaged into multiple deliverable components. In one of those components, component A, the ids should be exported for runtime reuse by other components. In other components, the ids should not be exported because all reuse is local (for example, the output is a single infocenter, or a helpset that has only one component).
- When author 1 builds component A, the author uses a map that exports the ids, rather
exporting the ids from the topic <prolog>.
<map> <topicref href="componentA/configA.dita"> <topicmeta> <exportanchors> <anchorid id="step1"/> <anchorid id="step2"/> <anchorid id="step3"/> </exportanchors> </topicmeta> </topicref> </map>
- The rest of the use case is the same as previous - the @conref reference is passed on to the runtime/display format to deal with, rather than being resolved during native DITA processing.
Delaying resolution for a topic
The ID on an <anchorid> element is first compared with the topic's id, and then with elements inside that topic. This results in the following situation.
<map> <topicref href="componentA/this.dita"> <topicmeta> <exportanchors> <anchorid id="this"/> <anchorid id="that"/> </exportanchors> </topicmeta> </topicref> </map> <topic id="this"> <title>This and that</title> <shortdesc>Oh, you know, this and that.</shortdesc> <body> <fig id="that"><p>more of that</p></fig> </body> </topic>
- The first ID to be exported is "this", which matches the topic id, so resolution of @conref values that target the topic should be delayed.
- The second value is "that", which matches a figure within the topic, so resolution of @conref values that target the figure should be delayed.
- Note that if the "this" is also used within the topic (which is legal from a DITA perspective), it will not be possible to export that id, because processors will match on the topic's id first.
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.
The following attributes are available on this element: Universal attribute group (with a narrowed definition of @id, given below), @keyref, and @outputclass.
- @id (REQUIRED)
- Indicates an ID within the specific topic that will be preserved during processing. Any @conref values referencing the indicated ID will not be resolved; when possible, the original relationship is preserved in any processed document. Note that this element creates an exception to the general rules that IDs can only be used once within a single topic or within a map; this is because the ID is actually a pointer to another target, rather than being a target itself. This attribute is defined with the XML Data Type CDATA.