The tag sets an attribute than will be used by other tags.
When setting an attribute in FaceletContext ( for example: context.setAttribute("x", new Object()); ) for the first time everything works OK.
But after that for any consequent ajax request, after re-setting the attribute the attribute value does not change!!!! I will be re-evaluated when a hole page refresh or an ordinary HTML request is made on the page.
In other words, the attribute is just set once (in the page first load) and never re-evaluated again.
I guess the facelet context is not re-evaluated on each A4J request.