A simple test follows:
${message} <#if message?exists>Message exists! #if>
Test normal includes:
<#include "test-included.html"> ${foo} ${nestedMessage}Test unparsed includes:
<#include "test-included.html" parse=false> <@twice> Kilroy @twice>Test subdir includes:
<#include "subdir/test-include-subdir.html">