title: Negate RE2 regular expression
body: <p>Could you please help me to understand if RE2 allows to negate regular expressions (the same effect as "<strong>grep -v</strong>", i.e. "select everything that does not match a given expression")?</p>
  
  <p>For example, I could match (positive match): </p>
  
  <pre><code>"[[:upper:]][[:upper:]][[:upper:]][[:digit:]]"
  </code></pre>
  
  <p>How do I select using RE2 everything that does not match the above expression (negative match)?</p>
  
  <p>Thank you for your help!</p>