The best reference can be found here:

 

http://www.openntf.org/xspext/xpages%20extension%20library%20documentation.nsf/xpages-doc/Controls.html 

 

In addition to all the components in the default runtime library (the xp namespace), the above page includes documentation for all components available in the XPages Extension Library ( http://extlib.openntf.org ). The tool that generates this documentation can be found at http://www.openntf.org/internal/home.nsf/project.xsp?action=openDocument&name=XPages%20Documentation%20Generator for use in documenting any custom components you develop.