Customizing DITA Open Toolkit
There are several ways to customize and extend the toolkit. You can adjust various aspects of the default output by setting parameters or using custom stylesheets. For more complex customizations, use custom DITA-OT plug-ins to override other parts of processing.
A single XSL file can be used as an override by passing it in as a parameter. For example, when building XHTML content, the XSL parameter allows users to specify a single local XSL file (inside or outside of the toolkit) that is called in place of the default XHTML code. Typically, this code imports the default processing code, and overrides a couple of processing routines. This approach is best when the override is very minimal, or when the style varies from build to build. However, any extension made with this sort of override is also possible with a plug-in.
Creating a plug-in can be very simple to very complex, and is generally the best method for changing or extending the toolkit. Plug-ins can be used to accomplish almost any modification that is needed for toolkit processing, from minor style tweaks to extensive, complicated new output formats.
Editing DITA-OT code directly is strongly discouraged. Modifying the code directly significantly increases the work and risk involved with future upgrades. It is also likely that such modifications will break plug-ins provided by others, limiting the functions available to the toolkit.