Each column is separated by '/', and is in the form 'nb_rows @ offset x repeat_count'. Nb_rows is the number of rows for this column. The offset is in mm and optional. Repeat_count is optional and repeats this column multiple times. Spaces are not important.For example '3x2 / 4@11' means we want 3 columns, the two first with 3 rows without offset, and the last with 4 rows starting at 11mm high.