title: Regex for matching certain numbers of digits
body: <p>The following regex will match the range 9-11 digits: <code>/\d{9,11}/</code></p>
  
  <p>What is the best way to write a regex matching exactly 9 <em>or</em> 11 digits (excluding 10)?</p>
  
  <p>Using the pattern attribute of an input element, thus the regex should match the entire value of the input field. I want to accept any number containing 9 or 11 digits.</p>