[xwiki-devs] Is there any document about how to extend the wysiwyg editor?

Hello ,I want to add a button which is not contained in xwiki by default, on the toolbar of the wysiwyg editor ,I have read the java source of it ,and still have some problems .So I want to know is there any document about this , for the plugin contains so complex and unfamiliar class to me that I was puzzled(Of course ,most of the reason is that I am a newbie in programmes. ) .Thank you .