There are a number of situations where you may need to redirect the browser based on the user agent of the browser. An example would be to an IE6 page, or a smartphone modified subdomain.
This article includes the PHP class I use for simple form validation. The intent is to use the class for simple web forms such as a contact us form. If you are working on something larger like an e-commerce site you need something more robust.
I'm hooked on using CodeIgniter which uses an active record class. This is bad because when I work on a non CodeIgniter project the work is not done for me. This article explains the PHP function I wrote which takes a Associative array and converts it into a mysql INSERT statement.
This is a brief introduction to PHP sessions. Creating sessions are very easy! Frameworks and CMSes usually have a built in class to handle PHP sessions, but today I was working on a project which didn't have such a class. Also this is a good article if you are just learning PHP. I wrote this article back in 2005.
Yesterday, I blogged about custom 404 pages using htaccess. In the apache article, I hinted that you should use your framework to handle the 404 page.
This article explains how to create a custom 404 page in CodeIgniter (PHP framework).