The @conaction attribute

There are three possible functions using the @conaction attribute: replacing an element, pushing content before an element, and pushing content after an element. The @conaction attribute always declares the desired function while the @conref attribute provides the target of the reference using the standard @conref syntax.

In each case, an element pushed using @conref must be of the same type as, or more specialized than, its target. If the pushed element is more specialized than the target, then it should be generalized when the @conref is resolved. This ensures that the content will be valid in the target topic.

• It is valid to push using @conref when the two elements involved are of the same type. For example, a <step> element can use the conref push feature with another <step> as the target of the @conref.
• The target element can be more general than the source. For example, it is legal to push a <step> element to replace a general list item (<li>); the <step> element should be generalized back to a list item during the process.
• It is not possible to push a more general element into a specialized context. For example, it is not legal to push a list item (<li>) in order to replace a <step>, because the list item allows many items that are not valid in the specialized context.

Replacing content in another topic

When the @conaction attribute is set to "pushreplace", the source element will replace the target specified on the @conref attribute. The pushed content remains in the source topic where it was originally authored.

<task id="example" xml:lang="en">
  <title>Example topic</title>
  <taskbody>
    <steps>
      <step id="a"><cmd>A</cmd></step>
      <step id="b"><cmd>B</cmd></step>
      <step id="c"><cmd>C</cmd></step>
    </steps>
  </taskbody>
</task>

<task id="other" xml:lang="en">
  ...
   <step conaction="pushreplace" 
         conref="example.dita#example/b">
     <cmd>Updated B</cmd>
   </step>
  ...
</task>

<task id="example" xml:lang="en">
  <title>Example topic</title>
  <taskbody>
    <steps>
      <step id="a"><cmd>A</cmd></step>
      <step id="b"><cmd>Updated B</cmd></step>
      <step id="c"><cmd>C</cmd></step>
    </steps>
  </taskbody>
</task>

When resolving a conref push action, attributes are resolved using the same precedence as for normal @conref, with one exception. Attributes on the element with the @conref attribute (in this case, the source doing the push) will take priority over those on the referenced element. The exception is that if the source element does not specify an ID, the ID on the referenced element remains; if the source element does specify an ID then that replaces the ID on the referenced element.

It is an error for two source topics to replace the same element. Applications MAY warn users if more than one element attempts to replace a single target.

Pushing content before or after another element

Setting the @conaction attribute to "pushbefore" allows an element to be pushed before the element referenced by the @conref attribute. Likewise, setting the @conaction attribute to "pushafter" allows an element to be pushed after the element referenced by the @conref attribute. Multiple sources can push content before or after the same target; the order in which that content is pushed is undefined.

When an element is pushed before or after a target, the resulting document will have at least two of that element. Because this is not always valid, a document attempting to push content before or after a target must take an extra step to ensure that the result will be valid. The extra step makes use of the conaction="mark" value.

When pushing before, the @conref attribute itself looks just as it did when replacing, but the @conaction attribute is set to "mark" because it is marking the target element. This element remains empty; its purpose is to ensure that it is legal to have more than one of the current element. Immediately before the element which marks the target, you will place the content that you actually want to push. This element will set the @conaction attribute to "pushbefore".

When pushing after, the procedure is the same, except that the order of the elements is reversed. The element with conaction="pushafter" comes immediately after the element which marks the target.

Attributes on the element which is pushed (the one with conaction="pushbefore") must be retained on the target, apart from the @conaction attribute itself. If this causes the result document to end up with duplicate IDs, an application can recover by dropping the duplicate ID, modifying it to ensure uniqueness, or warning the user.

When content is pushed from one topic to another, it is still rendered in the original context. Processors might delete the empty element that has the conaction="mark" attribute. In order to push content from a topic without actually rendering that topic on its own, the topic should be referenced from the map with the @processing-role attribute set to "resource-only".

Combining @conaction with @conkeyref or @conrefend

The @conkeyref attribute can be used as an indirect way to specify a @conref target. If the @conkeyref attribute is specified on an element that also uses the @conaction attribute, the @conkeyref attribute is used to determine the target of the conref push (as it would normally be used to determine the target of @conref).

The conref push function does not provide the ability to push a range of elements, so it is an error to specify the @conrefend attribute together with the @conaction attribute. If the two are specified together an application can recover by warning the user, ignoring the @conrefend attribute, or with some other implementation strategy.