Apps what is this widget called in the Ancestry app


I'm currently writing my first app for a tablet and want to use a similar mechinism to the Ancestry app (free in the play store) to display left and right hand panels.

I think these panels are fragments, which are enabled through a gessture. However if they are I don't understand how Ancestry got them to work in this manner - i.e. taking up space on the main layout rather than floating over it. Any ideas or tutorials on this?

Many thanks.