JSF - composition - get UIPanel(s) by class name

I just watched the answer but I don't get it... the snippet as (snippet A):

@FacesComponent("ticker")
public class UITicker extends UIPanel {

the thing is I am not sure what it does in generated code :( I mean does it takes h:panelGroup the upper tag of composition (see snippet B):

<ui:composition>
<h:panelGroup layout="block">
</h:panelGroup>
</ui:composition>

...or (comment here please) ?

So my question is what the snippet A does and how to get h:panelGroup of snippet B?

Thanks

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