Here is a concise example of ReflectionFunction usage for Parameter Reflection / introspection (e.g. to automatically generate API descriptions)

<?php
$properties = $reflector->getProperties();
$refFunc = new ReflectionFunction('preg_replace');
foreach( $refFunc->getParameters() as $param ){
    //invokes ■ReflectionParameter::__toString
    print $param;
}
?>

prints:

Parameter #0 [ <required> $regex ]
Parameter #1 [ <required> $replace ]
Parameter #2 [ <required> $subject ]
Parameter #3 [ <optional> $limit ]
Parameter #4 [ <optional> &$count ]