Files listed in the javax.faces.CONFIG_FILES initialization parameter inside WEB-INF/web.xml. For example,

<web-app>
   <context-param>
      <param-name>javax.faces.CONFIG_FILES</param-name>
      <param-value>WEB-INF/navigation.xml,WEB-INF/beans.xml</param-value>
   </context-param>
   
</web-app>

(This mechanism is attractive for builder tools because it separates navigation, beans, etc.)