XtSetValues then calls the constraint set_values procedures so that the parent can recompute derived constraint set_values procedures so that the parent can recompute derived constraint fields and move or resize the child as appropriate.
These are stored as vector graphics so you can resize them without any loss of quality.
Controls are also provided to allow the user to dynamically resize the individual panes.
To resize a floating control bar move the mouse pointer over the edge of the control bar window.
For more details on which pane it chooses to resize, see layout semantics.