Note that if you do a "view source" in your browser, you cannot immediately see how SSI works, because it looks as if the contents of navigation.html have been "cut and pasted" into the source of all three HTML files.
The only way to really see what is going on is to look at the files through a different server---one that does NOT do the interpretation of the SSIs.
You can do that by using the secure file transfer server instead of the web server to download the HTML files.
Open up the SSH Secure File Transfer Client (or a similar secure file transfer program, such as Fetch on the Mac).
Connect to copland.udel.edu with your UD username and password. On the server side, after logging in, the program will probably start you out by default in your home directory on copland.udel.edu (e.g. something like /home/usra/d9/55560—yours will be different, but it will have the same format).
Navigate instead to this directory:
/www/htdocs/CIS/103/pconrad/06F/examples/HTML/ssi
You should then be able to download the files in a way that does NOT interpret the SSI directives inside—you are getting the files as they actually are on the server side.
As a result, if you look inside any of the following files...
mainPage.shtmlviewingSource.shtmllinks.shtml
... instead of seeing the HTML for the common navigation header (a <div>
element) as the first thing inside the <body> element, you'll see instead the following line:
<!--#include file="navigation.html"-->That is the line that essentially "cuts and pastes" the contents of
navigation.html into the file at that point.