Why would we want to type hint variables via php doc

phpdoc-var-type.php

<?php
/**
Here is an example of type hinting variables (not function parameters), using php doc.
There is only one reason for doing this - to let IDEs know what is what.
*/

class X{
    public function blahx(){
        echo 'blahx';
    }
}

class Y{
    public function blahy(){
        echo 'blahy';
    }
}

/**
 * This func. will return instance of X or Y class, depending on the $what param.
*/
function getMeSth($what){
    if($what == 'x'){
        return new X();
    }    
    if($what == 'y'){
        return new Y();
    }    
    throw new Exception('oh oh oh');
}

/*
 * getMeSth() will return instance of X or Y class depending on our decision in runtime. IDE have no idea,
 * what it will actually return. So, no code completion support, but...
 * thanks to the below lines, IDE knows what is the type of $sth - in this case, that is class X:
 */

/**
 *@var X $sth
*/
$sth = getMeSth('x');
//and we have code completion in most IDEs
$sth->blahx();