displays 1 to 6 child blocks on the same line
syntax 1 : {up cell=x1-x2}content with 2 child blocks{/up cell}
syntax 2 : {up cell=x1-x2} cell-1 content {======} cell-2 content{/up cell}
x1-x2 are the widths based on a grid of 12 columns
example : cell=6-6 for 2 equal columns.
The widths of the UP-width class are used