rmal manner by allowing the tag library author to indicate in the description subelement an
 observable type. The type should be a subtype of the tag handler implementation class or void. This addititional
 constraint can be exploited by a specialized container that knows about that specific tag library, as in the case
 of the JSP standard tag library.

 <p>
 When a tag library author provides information on the observable type of a tag handler, client programmatic code
 should adhere to that constraint. Sp