Day Planner (0.10 and later) includes a plugin system, allowing anyone to easily extend and alter Day Planner without having to patch the source. It includes a plugin packaging system, making it easy to install and remove plugins at any time

To get started with plugin development, grab the Day Planner source tarball or check out the git repository.

From there you can access an example/tutorial plugin as ./plugins/HelloWorld.pm. It serves as a quick introduction to the plugin system.

For the full API documentation, run
  perldoc ./modules/DP-CoreModules/lib/DP/CoreModules/Plugin.pm
Day Planner also comes with a utility script that will autogenerate the plugin package, run
  ./devel-tools/plugin_package [path to plugin]
If you just need to make the metadata file, run
  ./devel-tools/plugin_mkmetafile [path to plugin]