PHP syntax explanation needed please

I've never ran across a statement like this before and I can't find a reference for it. I was wondering if anyone has and/or could explain it.

Basically I have two variables that are just storing counts ($var1 and $var2).

In this function this statement exists.
$var1+=$var2;

Anybody have a clue? Thanks

 

It's the same as

$var1 = $var1 + $var2;

 

Oh ok.. cool. Thanks Joshua

 

Really there are a lot of ops which can be written in same way

$A +=$B => $A = $A + $B
$A -=$B => $A = $A - $B
$A *=$B => $A = $A * $B
$A /=$B => $A = $A / $B
$A &=$B => $A = $A & $B
$A |=$B => $A = $A | $B
$A ^=$B => $A = $A ^ $B

Code (markup):