title: PHP_OS - does it contain OS it was built on or runs on?
body: <p>I searched for quite a while now, but i could not find a definite answer to the question wether the constant PHP_OS contains the OS php was built on or runs on.</p>
  
  <p>The php documentation of php_uname (<a href="http://php.net/manual/de/function.php-uname.php" rel="nofollow">http://php.net/manual/de/function.php-uname.php</a>) states:
  "For the name of just the operating system, consider using the PHP_OS constant, but keep in mind this constant will contain the operating system PHP was <strong><em>built on</em></strong>. "</p>
  
  <p>However, on the very same page there is a comment from 2006 stating:
  "Contrary to the last note, PHP_OS does display the OS PHP runs on currently, [...] This has nothing to do with the system PHP was built on."</p>
  
  <p>I could not find any definite answer anywhere on the web regarding this question (topis about php_uname and PHP_OS mostly only cover os detection and similar topics). What's right now - the documentation or the comment?</p>
  
  <p>The pear-core package uses PHP_OS to determine wether it's <strong><em>running</em></strong> on Unix-like systems or on windows, so is it safe to assume the documentation is indeed wrong?</p>