Plug-in use cases 
  Plug-ins allow you to extend the functionality of DITA-OT. This might entail adding support for specialized
    document types, integrating processing overrides, or defining new output transformations.
  
Setting parameters with plug-ins Adding a new target to the Ant build process ant.import extension point can be used to make new targets     available to the Ant processing pipeline. This can be done as part of creating a new transformation, extending     pre-processing, or simply to make new Ant targets available to other plug-ins.Adding an Ant target to the pre-processing pipeline Adding a new transformation type Processing topics with XSLT in preprocess Adding parameters to existing XSLT steps <xsl:param> values within XSLT overrides.Overriding an XSLT-processing step Adding a Java library to the classpath dita.conductor.lib.import extension point to add an additional Java     library to the DITA-OT classpath  parameter.Adding new diagnostic messages dita.xsl.messages extension point to add plug-in-specific messages to the     diagnostic messages that are generated by DITA-OT. These messages then can be used by any XSLT override.Creating a new plug-in extension point _template" to the filename before the file suffix. When the plug-in is installed, this file will     be processed like the built-in DITA-OT templates.Extending an XML catalog file Adjusting file names in map-first pre-processing preprocess2), you can create a custom plug-in and specify the code that contains your custom     rewrite rules.Adding Saxon customizations <pipeline> task with custom XSLT.