Logical operators - 'or' vs. '||' (double pipe) in PHP

The two different versions operate at different precedences:

http://www.php.net/manual/en/language.operators.precedence.php

The "spelled out" operators and and or have lower precedence, even lower than assignment, so you may use them to avoid having to write parentheses in so many places. For example:

$d=$a||$b and $c is equivalent to ($d=$a||$b) && $c

They are also more readable in many contexts.