DITA Open Toolkit provides a series of extension points that can be used to integrate changes into the core code. Extension points are defined in the plugin.xml file for each plug-in. When plug-ins are installed, DITA-OT makes each extension visible to the rest of the toolkit. extension pointsoverviewplug-in extension pointspreprocessing plugin.xml topicmergeorg.dita.pdf2.xsl.topicmerge