Question : directing all page requests to handlepagereq.php

I have inherted a php mysql site which I am unpicking to understand how it works.
Some pages are static html, some are created dynamically  with PHP / Mysql on a hosted apache server.
The .htaccess file for the main directory has  the  content laid out here between the pecked lines:-
-------------------------------------------------------------
RewriteEngine On
RewriteBase /

RewriteRule ^[^/]+.html$ handlepagereq.php [PT]


DirectoryIndex ./handlepagereq.php
--------------------------------------------------------------------------

I think that this code does one of two things. Either
a)Drives ALL page requests to handlepagereq.php  (which displays the home page if an invalid page request is entered) regardless of whether the requested page exists on the server.
b)Drives All page requests to handlepagereq.php EXCEPT those static pages which exist (e.g. AboutUs.htm).  I do know that for those which don't exist,  the handlepagereq.php then either generates the pages with mysql//php if a valid page request is made, or  else displays the home page if an invalid request is made.

Can someone tell me if I am right and if so, whether it is a) or b) ?

In any case can someone put into plain English the command:-

 RewriteRule ^[^/]+.html$ handlepagereq.php [PT]

Answer : directing all page requests to handlepagereq.php

Oh, reference site: http://httpd.apache.org/docs/current/custom-error.html