title: Jquery add css but don´t ovverwrite old value
body: <p>for a little CSS3 font Tester I have several checkboxes to add Opentype stylisticSet features to a textarea. Currentliy I´m doing this by adding a class with jquery like:</p>
  
  <pre><code>$( "#fontform" ).addClass( "ss01" );
  </code></pre>
  
  <p>where class looks like:</p>
  
  <pre><code>.ss01 {
      -moz-font-feature-settings: "ss01";
      -webkit-font-feature-settings: "ss01";
      font-feature-settings: "ss01";
  }
  </code></pre>
  
  <p>The Problem with this is if one clicks the next checkbox f.e. for ss02 the previous value of <code>font-feature-settings</code> is overwritten. Is there some way with jquery to add the value like:</p>
  
  <pre><code>.appliedstylies {
      -moz-font-feature-settings: "ss01","ss02";
      -webkit-font-feature-settings: "ss01","ss02";
      font-feature-settings: "ss01","ss02";
  }
  </code></pre>
  
  <p>thanks!</p>