In frameworks like Zend Framework (or extensions of it), it is sometimes possible to pass information like type hints to the framework code by using PHPDoc style comments.
I cannot imagine that the framework parses the files using PHP, but I do not see any other way to achieve this, except for some built-in language feature of PHP, which I don't know of. So how is this done?
They use reflection and especially ReflectionMethod::getDocComment() (there is also ReflectionClass::getDocComment(), ReflectionProperty::getDocComment() and ReflectionFunction::getDocComment()). The rest is simple: just parse the doc-block with some regular expressions or something like that.