nl_tokens: Positions the overlay elements : top middle & bottom .
pl_tokens: function OverlayLayout ( context , options ) { var height = ( context . size [ 1 ] - options . itemSize ) / 2 ; context . set ( 'top' , { size : [ context . size [ 0 ] , height ] , translate : [ 0 , 0 , 1 ] } ) ; context . set ( 'middle' , { size : [ context . size [ 0 ] , context . size [ 1 ] - ( height * 2 ) ] , translate : [ 0 , height , 1 ] } ) ; context . set ( 'bottom' , { size : [ context . size [ 0 ] , height ] , translate : [ 0 , context . size [ 1 ] - <mask> , 1 ] } ) ; }