$blaa = array_key_exists('blaa', $_GET) ? $_GET['blaa'] : "blee" ; echo '$blaa' ;
...you can type ?blaa=abc at the end of a url to change the echoed word in the site to abc...etc
i'm very worried about security though. i tried injecting some dodgy code into the url and found the quotes were automatically backslashed somehow, but my injection skills are not as good as some hackers. should i be using some functions to strip bad input? if so, what exactly should i use?