<A target="_blank" href="http://www.juliusbuss.de/web/youatnotes/blog-jb.nsf/dx/use-a-nice-dijit.form.combobox-in-8.5.1-and-without-the-openntf-extension-library.htm">Julian Buss has posted some information on using dijit.form.Combobox</A> without the OpenNTF Extension Library. He's included the code for a function to make it work.