The available constraints are shown in the listbox. When a constraint is selected in the listbox the choices for that constraint will appear in the window.
When a constraint is selected, all lines that are constrained will be grouped together and displayed below the non-constrained lines. Constrained lines will appear in red in the Main Window listbox. If the Move Reserve Lines to Bottom or Move Blank Lines to Bottom options are selected in the Sort Prefs window, then these will be displayed after the constrained lines. Constrained lines are sorted as a group using the selected sort preferences in the Sort Prefs window.