just check out this code this may be helpful to understand the thing
Test1.jsp
------------------------------------------------------------------
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<HTML>
<HEAD>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<META name="GENERATOR" content="IBM Software Development Platform">
<META http-equiv="Content-Style-Type" content="text/css">
<LINK href="theme/Master.css" rel="stylesheet" type="text/css">
<TITLE>Test1.jsp</TITLE>
</HEAD>
<BODY>
<
jsp:include page="Test.jspf">
<jsp

aram name="test" value="First Paramter" />
<jsp

aram name="second" value="Second Paramter"/>
</jsp:include>
</BODY>
</HTML>
Test.jsp
-----------------------------------------------------------------
<p> The first parameter is ${param.test} </p>
<p>The second parameter is ${param.second}</p>
<jsp:include page="test2.jsp"/>
Test2.jsp
----------------------------------------------------------------------
<p> I am in
test 2 </p>
Now if you execute the file test1 you will get the expected result . But just change the extension of Test.jsp to Test.jspf. Then try to execute the same.
You will find , while changing the extension of test.jsp to jspf the scripts are the executed. That is the thing they have mentioned in the paragraf.