This may optionally specify a display width for the left pane, using the same column units used by the dspwid parameter (for defining column widths). If zero, then XTREE will try to determine the optimum width by adding up the optimum display widths of the initially visible rows. You can also set it to -1 (or 255) to put the splitter bar separating the panes exactly in the middle of the XTREE.

If you specify a size that is too wide, the left pane will initially occupy the entire XTREE but the user will still be able to move the splitter bar from the right edge to make the right pane visible.

If you specify a negative value (other than -1), it acts the same as if it had been positive, except that the left pane horizontal scroll bar will be based on the specified width. This generally has the effect of initially graying out the scroll bar, which is usually desirable.