[PHP] string concatination

[Matthew Oatham]

Hi, 

What is the correct way, using php to join to strings, vars or other wise.

i.e. how do I join

$string1 = "hello";
$string2 = "world";

do i do

$string1 . $string2;

and what about ..

$string2 = $string1 . "world";

Is that correct?