User blog comment:BertH/Fluid layout is arriving on December 4/@comment-26454032-20131202215617/@comment-4957813-20131202220140

It is mandatory, basically when resizing the window, the content within the window changes and alters to match. You can play around with it on CC by resizing the current window. This is done to accomodate the increasing number of users who use mobile devices like tablets and smartphones to work on the wikis.