As Johannes Schluter mentions in his latest blog post, another new feature has been added to the trunk of the PHP project - scalar type hints.
So in my blog series I try to cover all additions to PHP trunk so I have to mention scalar type hints.
He gives examples of both simple hinting (ensuring a value is a float) and a more complex example setting an attribute on a PDO connection (checking for an integer). Sample error messages are included as well. He also gives some advice on mixing strong and weak typing in your apps - it's like "opening a can of worms".