title: Uppercase Booleans vs. Lowercase in PHP
body: <p>When I was learning PHP, I read somewhere that you should always use the upper case versions of booleans, <code>TRUE</code> and <code>FALSE</code>, because the "normal" lowercase versions, <code>true</code> and <code>false</code>, weren't "safe" to use.</p>
  
  <p>It's now been many years, and every PHP script I've written uses the uppercase version. Now, though, I am questioning that, as I have seen plenty of PHP written with the lowercase version (i.e. Zend Framework).</p>
  
  <p>Is/Was there ever a reason to use the uppercase version, or is it perfectly OK to use the lowercase?</p>
  
  <p>edit: Forgot to mention that this applies to <code>NULL</code> and <code>null</code> as well.</p>