The 'JAX-RS Application' is the top level fragment of the URI Path Templates of the JAX-RS Endpoints.
One way to configure it is in the webapp's deployment descriptor, with something like this:

<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    <servlet-mapping>
        <servlet-name>javax.ws.rs.core.Application</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>

see JBossAS 7 / JAX-RS docs here

Hélas, the web.xml validator reports an error (or a warning) with the following message

servlet-name references to javax.ws.rs.core.Application that is not a servlet

For sure, the validation level could be set to ignore, but could this JAX-RS specific rule be implemented by default ?