For full and up to date documentation API look on AUI Docs
This short form has right-aligned buttons such as you might see in a Dialog. Its .buttons-container has a class of .right and the buttons are thus aligned right. It is shaded only to show the width of the form.
You can also have a description here if you like
The visible legend is optional - you may not want it for the single checkbox. You can make it an assistive legend (view source to see it).