You may have heard something about operator priority before, for example that 1+2*3 results in 7 and not 9 (You always calculate first * and / and after that + and -). So in PHP the order of AND and OR statements is:

1. &&
3. AND
4. XOR
5. OR

Example:

<?php
    // That's the same as $a||($b&&$C)
    $a || $b && $C;
    // That's the same as ($a||$b)&&$C
    $a || $b AND $C;
?>

AND, XOR and OR are the lowest operators in PHP. So, all other operators are executed first.