title: Regex: Matching by exclusion, without look-ahead - is it possible?
body: <p>In some regex flavors, [negative] zero-width assertions (look-ahead/look-behind) are not supported. </p>
  
  <p>This makes it extremely difficult (impossible?) to state an exclusion. For example "every line that <em>does not</em> have "foo" on it", like this:</p>
  
  <pre><code>^((?!foo).)*$
  </code></pre>
  
  <p>Can the same thing be achieved without using look-around at all (complexity and performance concerns set aside for the moment)?</p>