YME exposes a bunch of Microsoft COM objects, which means that any language which allows you to use COM will work as a basis for writing plugins to the application. For example, you may write a Visual Basic or C++ plugin that users can download and install, or you can embed Javascript calls to the media player objects inside your web pages, thus controlling the media player directly from the web! Pretty much anything you can do with a native installable plugin can be done via Javascript web pages. When your plugin is active it has full control over the entire right-pane window of the application, and may do whatever you want it to. We provide you the playground and the sandbox, you build the castles!
Every usable object and interface is fully documented and referenced via the links at the top of these pages. You may also find lots of help (including discussions, archives, and samples) from the YME Developer's Group: http://groups.yahoo.com/group/ymedev/ . If you're just getting started, you should check out: