<para> This is useful for making a column heading span across more than one column, e.g. if you had to columns next to each other, UserId and UserName then you could make the UserId column heading 'User', the UserName column heading blank and let the UserId column span 2 columns so that it can flow into the space occupied by the UserName column. </para> <para> A value of -1 indicates that the heading should span across to the right until it meets another heading. This will only ever be the case if this is a stacked column. </para> <para> A value of zero or 1 indicates that no spanning should occur. </para> <para> Column spanning will only work correctly for left-aligned columns. </para>