David Coallier has posted a nice overview of what SPL Types are in PHP and a brief example of hos they can be used.

I got karma to SPL_Types and added a new SplFloat() object, a few warning typos and more "flexible" strict modes for different types.

SPL_Types are a way to make PHP strongly typed (no adapting variables) to help make a PHP application "more correct" by forcing the variable's type to stay the same. His example shows the creation of a few variables with these new methods and how they can be used, both correctly and incorrectly.