title: Blacklist, case-insensitive regex for client-side validation
body: <p>I'd like to implement some client-side validation for a case-insensitive, blacklisting of variations on a word. For example, if the word in question is <code>Dog</code>, a user should not be able to enter any variation of it:</p>
  
  <pre><code>dog
  doG
  dOg
  dOG
  Dog
  DoG
  DOg
  DOG
  </code></pre>
  
  <p>Was trying to experiment with a negative lookahead, i.e., <code>^(?!.*(?:dog|doG|dOg|dOG|Dog|DoG|DOg|DOG))</code> but that seems too verbose and not generic enough.</p>