Plug-in dependencies
A DITA-OT plug-in can be dependent on other plug-ins. Prerequisite plug-ins are installed first, which ensures that DITA-OT handles XSLT overrides correctly.
The require element in the plugin.xml file specifies whether the plug-in has dependencies. Use require elements to specify prerequisite plug-ins, in order from most general to most specific.
If a prerequisite plug-in is missing, DITA-OT prints a warning during installation. To suppress the warning but keep the installation order if both plug-ins are present, add importance="optional" to the require element.
If a plug-in can depend on any one of several optional plug-ins, separate the plug-in IDs with a vertical bar. This is most useful when combined with importance="optional".
Example: Plug-in with a prerequisite plug-in
The following plug-in will only be installed if the plug-in with the ID com.example.primary is available. If that plug-in is not available, a warning is generated and the installation operation fails.
<plugin id="com.example.builds-on-primary">
<!-- ... Extensions here -->
<require plugin="com.example.primary"/>
</plugin>
Example: Plug-in that has optional plug-ins
The following plug-in will only be installed if either the plug-in with the ID pluginA or the plug-in with the ID pluginB is available. If neither of those plug-ins are installed, a warning is generated but the installation operation is completed.
<plugin id="pluginC">
<!-- ...extensions here -->
<require plugin="pluginA|pluginB" importance="optional"/>
</plugin>
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