title: Add css when @media print using less mixin and guard expressions
body: <p>I want to avoid duplication in my code. Is it possible to write something like this in LESS?</p>
  
  <pre><code>.print when (@media print = true) {
      background: @heading-background-color !important;
      -webkit-print-color-adjust: exact;
   }
  
    .header-month {
      .print
      background: @heading-background-color;
      font-weight: bold;
    }
  </code></pre>
  
  <p>Instead of:</p>
  
  <pre><code>@media print {
    .header-month {
      background: @heading-background-color !important;
      -webkit-print-color-adjust: exact;
    }
  }
  
    .header-month {
      background: @heading-background-color;
      font-weight: bold;
    }
  </code></pre>
  
  <p>It doesn't look like an improvement here. But I'm working with multiple classes and need to do this for all of them.. So maybe an alternative if this is not possible?</p>