Two legends in a fieldset

You can do that by adding an extra element and positioning it absolutly in the <fieldset> :

fieldset {
  position: relative;
}
.legend2 {
  position: absolute;
  top: -0.2em;
  right: 20px;
  background: #fff;
  line-height:1.2em;
}

<fieldset>
  <legend>
    Some Text
  </legend>
  <div class="legend2">Some other Text</div>
</fieldset>

You can use :after pseudo selector to achieve this. SEE THE DEMO. This way, you don't have to use any additional html tags.

fieldset {
    position: relative;
}

fieldset:after {
    content: "Some Text";
    position: absolute;
    margin-top: -25px;
    right: 10px;
    background: #fff;
    padding: 0 5px;
}