HtmlBasicRenderer

package javax.faces.render;

/**
 * <B>HtmlBasicRenderer</B> is a base class for implementing renderers
 * for HtmlBasicRenderKit.
 */

public abstract class HtmlBasicRenderer extends Renderer {

    @Override
    public void decode(FacesContext context, UIComponent component) {

        [...]
        if (clientId == null) {
            clientId = component.getClientId(context);
        }

        assert(clientId != null);
        Map<String, String> requestMap = context.getExternalContext().getRequestParameterMap();
        // Don't overwrite the value unless you have to!
        String newValue = requestMap.get(clientId);
        if (newValue != null) {
            setSubmittedValue(component, newValue);
        }
    }
}