PHP navigational menu with 'Current Page' class based on filename and query string

General information for the website: Simple ecommerce store
Description of requirements/features: I need a PHP-driven navigational menu which will automatically assign Class="currentPage" to the menu item corresponding to the current page. The HTML for the navigational menu can be a simple unordered list.

I'm comfortable with CSS/HTML but need help with the PHP.

The list of pages is:

Menu Item URL
-------------------------------------------------------------------------------
Page 1 http://mydomain/index.php
Page 2 http://mydomain/about.php
Page 3 http://mydomain/products.php
Page 4 http://mydomain/products.php?scri=30
Page 5 http://mydomain/products.php?&scri=31
Page 6 http://mydomain/products.php?&scri=32
Page 7 http://mydomain/cart.php

Some of the menu items can be matched to the page simply by matching the php file name, e.g. index.php would match 'Page 1'.

Other menu items need to be matched based on the contents of the Query String. For example:

products.php?scri=30 matches 'Page 4'
products.php?scri=31 matches 'Page 5'.

Further, the Query String parameter 'scri' potentially contains MULTIPLE values in ANY order, e.g.

products.php?scri=30,9,1
products.php?scri=9,4,1,30

In this example, therefore, the PHP code should look for the value '30' for parameter 'scri' anywhere in the Query String and match that to 'Page 4'.
Extra notes: