On this page: http://www.visual-paradigm.com/product/vpuml/faq.jsp
The Plug-in User’s Guide and API links to http://127.0.0.1/support/documents/vpumluserguide.jsp?pt=11&ch=4 . I assume the link is supposed to be http://www.visual-paradigm.com/support/documents/vpumluserguide/251/254/7039_introduction.html .