title: Finding match by negating (based on a missing string)
body: <p>I've been googling a lot about this.
  What I'm trying to achieve is the next:
  I have to check in a regex condition if a MIME is NOT of a specific type.</p>
  
  <p>For example, I have recevied the next message:</p>
  
  <pre><code>image/png, image/jpeg, document/pdf
  </code></pre>
  
  <p>I would like to detect the <code>document/pdf</code> part only
  , which is a MIME type, a string, that does NOT start with image/</p>
  
  <p>But no matter how hard I looked, tried and played around with the RegExBody software, I just utterly fail to match it..</p>
  
  <p>I'm posting this in despair and hopes that maybe an expert regex could help me out.. </p>
  
  <p>I tried many approaches, mainly:
  Finding out the non-image type, regardless if there is one or not.</p>
  
  <p>It just refuses to work.
  I tried positive lookahead and negative lookahead. But I probably used it wrong somehow. I can't post the examples because I have tried and deleted so many. The one that seemed really close to working was <code>\b(?:(?!image/\w+))\w+\b</code> but it just persists on selecting the second part of the non-matching pattern. 
  If I use: <code>image/png</code>
  It gets the: <code>png</code>
  Which means it would still return true although I meant it to ignore <code>image/</code> types..</p>