Use this tag—which is very similar to JSP's jsp:include—to encapsulate and reuse content among multiple XHTML pages. There are three things this tag can include: plain XHTML, and XHTML pages that have either a composition tag or a component tag.

You supply a filename, through ui:include's src attribute for JSF to include. That filename is relative to the XHTML file that was rendered as a result of the last request. So, for example, if JSF loaded the view login.xhtml, and that file included pageDecorations/header.xhtml, and pageDecorations/header.xhtml included companyLogo.xhtml, then companyLogo.xhtml will not be found if it's in the pageDecorations directory, because companyLogo.xhtml has to be in the same directory as login.xhtml.