title: Regular expression: find range except for one letter or a range
body: <p>How can I use the negation within square brackets as an exception, to find e. g. everything between a-z except for the the range from m-o? <code>[a-z^m-o]</code>?</p>
  
  <p>By the way: it's not for the sake of this example that I ask, but to be able to exclude ranges within ranges, or even single letters within ranges. I am pretty much aware that in this example it can be calculated.</p>
  
  <p>I use the Zend engine (PHP).</p>