title: How do I combine these 2 regex patterns into one using logical AND?
body: <p>I have 2 regexes: <code>[CD]\d\d(\.\d(\d)?)?</code> and <code>(?!C7[789])</code></p>
  
  <p>I want to accept <code>D77</code>, <code>D78</code>, <code>D79</code> but NOT <code>C77</code>, <code>C78</code>, <code>C79</code>.</p>
  
  <p>Thank you.</p>