That's a multipart response [0]. In the early days of 3G (and multimedia phones) we used to use those for some models of phone which supported it to give a better browsing experience - the gamble being that more downstream data would be faster than costing a request / response round-trip if you were pretty confident that the phone was going to ask for it.

[0] http://stackoverflow.com/questions/1806228/browser-support-o...