title: Find literal string in with PHP and REGEX
body: <p>This is my first time using REGEX with preg_match and I'm not at all experienced with REGEX anyways. So I'm trying to find the string (case insensitive) <code>def</code> possibly followed by a string in an input. The regex I'm using is: <code>(?-i)def?\.</code></p>
  
  <p>I get the following error: <code>Warning: preg_match(): Unknown modifier 'd' in /var/www/process.php on line 11</code></p>
  
  <p>When inputting: <code>asdsa saj dasjdkj def ddas</code></p>
  
  <p>and the same error with any other input.</p>
  
  <p>So what am I messing up with here? Is there some simple fix? </p>
  
  <p>Sorry if this seems to silly but I'm a baby chick in this area of PHP.</p>