title: Difference between NULL and null in PHP
body: <p>Is there a difference between <code>NULL</code> and <code>null</code> in PHP? Sometimes they seem to be interchangeable and sometimes not.</p>
  
  <p>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...</p>