title: LESS mix variable into attribute name in an attribute selector expression
body: <p>How can I implement the following syntax correctly?</p>
  
  <pre><code>.jacket(@classname, @attrname, @value) {
      .class-prefix-@{classname}[some-prefix-@{attrname}~="@{value}"] {
          //                                 ^Error From Here
          // Attributes
      }
  }
  </code></pre>
  
  <p>lessc shows that there is an <code>SyntaxError: expected ']' got '@'</code></p>