Use the following code to create a basic inputEx UrlField.
new Y.inputEx.UrlField({parentEl: 'container1', showMsg: true, value: 'http://ajaxian.com/archives/inputex-json-form-builder'});
If you use https, you might need to remove the favicon option (or provide a proxy).
new Y.inputEx.UrlField({parentEl: 'container2', showMsg: true, favicon: false, value: 'http://www.ajaxian.com'});
You can use all the parameters from StringField, including "typeInvite":
new Y.inputEx.UrlField({parentEl: 'container3', showMsg: true, favicon: false, typeInvite: 'webservice url'});