i notice there's this functionality on 9gag.com. on the homepage, the 'Y u no signup' button is on the right. but as you scroll down, the button is hooked onto the header banner. how is this done?? this can be also seen on this very page whereby the yellow panel(similar Questions) on the right freeze when u scroll this page down. in facebook timeline, as you scroll down there will be a absolute div which appear on the top which contain options for timeline, now, status, photo, place and event.

r they using javascript or is this something new in html5??