This is what is displayed when the file dir1/dir2/a/index.html is downloaded to your web browser. Note the heading "Page A" above appears automagically and is the contents of the file dir1/dir2/a/.title.
Note the link "Page A" in the link heading is explicitly
<a href='/more/toolbox/html/dir1/dir2/a/'>Page A</a>
The href URL does not include "index.html", as the browser inserts that automagically. Also note the href URL does not include the protocol (https) nor the server (math.temple.edu) as these are inherited from the current page.
The contents of this file are
<!--#include virtual='/cgi-bin/get_header' --> <!--#include virtual='/cgi-bin/get_dir_heading?uri=/more/toolbox/html/dir1/dir2/' --> (CONTENT) <!--#include virtual='/cgi-bin/get_footer' -->