Difference between NULL and null in PHP

Question

Is there a difference between NULL and null in PHP? Sometimes they seem to be interchangeable and sometimes not.

edit: for some reason when I read the documentation linked to in the answer (before posting this question) I read it as "case sensitive" instead of "case insensitive" which was the whole reason I posted this question in the first place...

Answer 1

Null is case insensitive.

From the documentation:

There is only one value of type null, and that is the case-insensitive keyword NULL.

Answer 2

There is no difference. Same type just its a case insensitive keyword. Same as True/False etc...

Answer 3

well there is a technical difference, just not what you're thinking (think: where does it appear in the dictionary): the ASCII value for lowercase null appears after the upper case. Try:

$a = NULL;
$b = null;
if($a < $b){
   print 'first num appears earlier in the dictionary than second num';
}
else {
   print'the right num appears in the dictionary before the left num ';
}

** actually there is no ASCII value for lower case null while upper case NULL is 0. lowercase null would be evaluated as a string value which would be greater than 0. The difference between all upper and lower case ASCII values is 32, except here where an entire string value is considered.