The docs you linked to are horribly out of date. You'll notice that they describe the Beta 3 build. I'll see to it that the docs there are updated. For now, use this link specifically to the RC build docs: http://dev.sencha.com/deploy/gxt-3.0...gxt/index.html. You can also use the documentation included in your download of the RC build zip archive. You'll find them in the "javadoc" directory.