title: negative grep with multiple elements
body: <p>Assuming the following code using grep     </p>
  
  <pre><code>grepl("XYz|Aba", results$category)
  </code></pre>
  
  <p>How to obtain the negative statement? </p>
  
  <p>I know that this is normally done using caret ^ but I don't seem to find the right syntax</p>