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> ## Registering a Custom Renderer with a Render Kit

> For every UI component that a render kit supports, the render kit defines a set of `Renderer` objects that can render the component in different ways to the client supported by the render kit. For example, the standard `UISelectOne` component class defines a component that allows a user to select one item from a group of items. This component can be rendered using the `Listbox` renderer, the `Menu` renderer, or the `Radio` renderer. Each renderer produces a different appearance for the component. The `Listbox` renderer renders a menu that can display an entire set of values. The `Menu` renderer renders a subset of all possible values. The `Radio` renderer renders a set of radio buttons.

> When the application developer creates a custom renderer, as described in Delegating Rendering to a Renderer, you must register it using the appropriate render kit. Because the image map application implements an HTML image map, `AreaRenderer` (as well as `MapRenderer`) should be registered using the HTML render kit.

> You register the renderer using the `render-kit` element of the application configuration resource file. Here is the configuration of `AreaRenderer` from the Duke's Bookstore application:

>     <render-kit>
>       <renderer>
>         <component-family>Area</component-family>
>         <renderer-type>DemoArea</renderer-type>
>         <renderer-class>
>           renderers.AreaRenderer
>         </renderer-class>
>         <attribute>
>           <attribute-name>onmouseout</attribute-name>
>           <attribute-class>java.lang.String</attribute-class>
>         </attribute>
>         <attribute>
>           <attribute-name>onmouseover</attribute-name>
>           <attribute-class>java.lang.String</attribute-class>
>         </attribute>
>         <attribute>
>           <attribute-name>styleClass</attribute-name>
>           <attribute-class>java.lang.String</attribute-class>
>         </attribute>
>       </renderer>
>       ...

> The `render-kit` element represents a `RenderKit` implementation. If no `render-kit-id` is specified, the default HTML render kit is assumed. The `renderer` element represents a `Renderer` implementation. By nesting the `renderer` element inside the `render-kit` element, you are registering the renderer with the `RenderKit` associated with the `render-kit` element.

> The `renderer-class` is the fully qualified class name of the `Renderer`.

> The `component-family` and `renderer-type` elements are used by a component to find renderers that can render it. The `component-family` identifier must match that returned by the component class's `getFamily` method. The `renderer-type` identifier must match that returned by the `getRendererType` method of the tag handler class. The component's configuration also needs to specify the component family and renderer type, which the next section explains.

> Each of the `attribute` tags specifies a render-dependent attribute and its type. The `attribute` element doesn't affect the runtime execution of your application. Instead, it provides information to tools about the attributes the `Renderer` supports.

> The object that is responsible for rendering a component (be it the component itself or a renderer to which the component delegates the rendering) can use facets to aid in the rendering process. These facets allow the custom component developer to control some aspects of rendering the component. Consider this custom component tag example:

>     <d:dataScroller>
>       <f:facet name="header">
>         <h:panelGroup>
>           <h:outputText value="Account Id"/>
>           <h:outputText value="Customer Name"/>
>           <h:outputText value="Total Sales"/>
>         </h:panelGroup>
>       </f:facet>
>       <f:facet name="next">
>         <h:panelGroup>
>           <h:outputText value="Next"/>
>           <h:graphicImage url="/images/arrow-right.gif" />
>         </h:panelGroup>
>       </f:facet>
>         ...
>     </d:dataScroller>

> The `dataScroller` component tag includes a component that will render the header and a component that will render the Next button. If the renderer associated with this component renders the facets you can include the following `facet` elements in the `renderer` element:

>     <facet>
>       <description>This facet renders as the
>         header of the table. It should be a panelGroup
>         with the same number of columns as the data
>       </description>
>       <display-name>header</display-name>
>       <facet-name>header</facet-name>
>     </facet>
>     <facet>
>       <description>This facet renders as the content
>         of the "next" button in the scroller. It should be a
>         panelGroup that includes an outputText tag that
>         has the text "Next" and a right arrow icon.
>       </description>
>       <display-name>Next</display-name>
>       <facet-name>next</facet-name>
>     </facet>

> If a component that supports facets provides its own rendering and you want to include `facet` elements in the application configuration resource file, you need to put them in the component's configuration rather than the renderer's configuration.

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