Check whether an extension is present in a fileset or an extensionSet. If the extension is present then a property is set.
Note that this task works with extensions as defined by the "Optional Package" specification. For more information about optional packages, see the document Optional Package Versioning in the documentation bundle for your Java2 Standard Edition package, in file guide/extensions/versioning.html or online at http://java.sun.com/j2se/1.3/docs/guide/extensions/versioning.html.
See the Extension and ExtensionSet documentation for further details