The two primary resources that control child positioning are XmNorientation and XmNpacking . XmNorientation determines whether RowColumn lays out its children in rows or columns. XmNpacking controls the general style of the layout. It proceeds until no more children fit along that dimension and then begins a new row or column. When placing children in a column, RowColumn does not alter their heights, but it makes the width of each child in the column equal to the width of the widest child in that column.
Analogous rules apply to row-major layouts.
RowColumn makes the width and height of each child identical. The width is the maximum width of all children, and the height is the maximum height. Unless XmNresizeWidth is False, it tries to grow large enough to enclose the greatest x extent of any child. Unless XmNresizeHeight is False, it tries to grow large enough to enclose the greatest y extent of any child. When this resource is True and the orientation is vertical, RowColumn increases the widths of children in the last column when necessary so that all children extend to the right edge of the RowColumn.