We need to use tag <ui:remove>
and </ui:remove>
between any JSF code that we want to comment it.
<ui:remove>
<h:outputLabel value="Yeah, I'm really commented" />
</ui:remove>
Of course you need add this xmlns to your header html tag. Check this minimal full example:
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:ui="http://java.sun.com/jsf/facelets">
<ui:remove>
<h:outputLabel value="Yeah, I'm really commented" />
</ui:remove>
</html>