Limit Child DIV Height to Parent DIV Height With Variable Sibling
===

I have a container DIV with a specified height, and contained within are two more DIVs, on for introductory copy that will vary (entered by the client), and another to list out various features. 

I want the features DIV to automatically fill the remaining space in the parent, and then scroll out the overflow.

How do I do that?

CSS:

    #article {
    width:940px;
    height:500px
    }
    
    #article-content {
    margin: 20px 0;
    }
    
    #article-features {
    height:100%;
    overflow-x: auto;
    }


http://jsfiddle.net/tylonius/Dw9EZ/