Working with Facelets
Facelets is a historical open source project written to manage web graphic templates and other utilities to write better web applications. It was started by the Apache community and is now integrated in JSF, so all its baggage can be used inside the application servers. The version supported by WildFly 10 and all Java EE 7 compliant application servers is 2.2. It is the candidate to write web templates, custom functions, and custom tags.
Web templates
Web templates allow us to create portions of pages that can be included several times in other pages. The common uses for them are the header and the footer of a website. We looked at the pages of Rubia Forums earlier. Here's the category page:

The breadcrumbs at the top are a header that can be shown on several pages. The same thing goes for the Powered by
image at the bottom. Now, see how to implement the header with the breadcrumbs starting with the category page:
<div ... xmlns:ui="http://java.sun.com/jsf/facelets"...