Apologies... the javadoc that came up in the value tip in eclipse told me
Annotations to control the importing of JavaScript stacks and libraries as well as stylesheets. This annotation may be placed on a class, in which case importing will occur as part of the SetupRender render phase. Alternately, the annotation maybe placed on any method (though typically it will be placed on a render phase method) and the import operations will be associated of that method.