title: How to check that a string contains at least 5 unique characters and is minimum 7 characters long?
body: <p>I need a validation that tests for a string that contains 5 unique characters and is at least 7 characters long.</p>
  
  <p>I have already tried it with the following regex:</p>
  
  <pre><code>^[a-zA-Z][0-9]{7}$  
  </code></pre>
  
  <p>I'm stuck and have no idea how to do the validation so that the string contains at least 5 unique characters.</p>