title: Double brackets in MathJax
body: <p>How can I achieve stretchy double brackets in MathJax using TeX?  For example,</p>
  
  <p><a href="https://i.stack.imgur.com/m9Yr0.png" rel="noreferrer"><img src="https://i.stack.imgur.com/m9Yr0.png" alt="Math using double brackets"></a></p>
  
  <p>The TeX package stmaryrd has this but MathJax doesn't support the import of arbitrary packages.</p>
  
  <p>I'd like the double brackets to look good at all sizes.</p>
  
  <p>Bonus: Is this possible in AsciiMath?</p>