У вашего броузера проблема в совместимости с HTML5
Straight from www.mycodeteacher.com! There are four ways to display strings in PHP. The "PHP Strings" lesson covers the four most common used methods of displaying strings to the web including how to parse specific string data using the explode function. This lesson will also teach you how to make your strings all upper and lower case using the strtoupper and strtolower functions while hitting on the basics of arrays in preparation of the following "PHP Arrays" tutorial.