(make-ui-constraint-class
        NAME
                string
        NUM-WINDOWS
                integer
        UI-CTR
                proc, 0 args
        CTR
                proc, NUM-WINDOWS args
        DRAW-PROC
                proc, 1+NUM-WINDOWS args, first arg #t for draw, #f for erase
        )
 returns a ui-constraint-class object
  -> probably just: (cons obid-ui-constraint-class (list NAME NUM-WINDOWS UI-CTR CTR DRAW-PROC))
  -> may side-effect a global list of constraint-classes created for the menu of ctrs

(ui-constraint-class? OBJECT)
 return #t iff OBJECT is a ui-constraint-class object

(ui-constraint-class-name UI-CONSTRAINT-CLASS) 
 returns NAME

(ui-constraint-class-num-windows UI-CONSTRAINT-CLASS)
 returns NUM-WINDOWS

(ui-constraint-class-ui-ctr UI-CONSTRAINT-CLASS)
 returns UI-CTR

(ui-constraint-class-ctr UI-CONSTRAINT-CLASS)
 returns CTR

(ui-constraint-class-draw-proc UI-CONSTRAINT-CLASS)
 returns DRAW-PROC

----

(make-ui-constraint UI-CONSTRAINT-CLASS)
 returns a ui-constraint-instance object
  -> probably just: (cons obid-ui-constraint (list CN ENABLE
UI-CONSTRAINT-CLASS LIST-OF-WINDOWS))
  -> may side-effect global list of UI-CONSTRAINTs

(add-ui-constraint UI-CONSTRAINT)
 adds UI-CONSTRAINT to the solver (adds its CN and sets ENABLE to true)

(remove-ui-constraint UI-CONSTRAINT)
 removes UI-CONSTRAINT from the solver (removes its CN and sets ENABLE to false)

(ui-constraint? OBJECT)
 return #t iff OBJECT is a ui-constraint instance object

(ui-constraint-windows UI-CONSTRAINT) 
 returns LIST-OF-WINDOWS

(ui-constraint-cn UI-CONSTRAINT)
 returns CN

(ui-constraint-enable UI-CONSTRAINT)
 returns ENABLE

(ui-constraint-class UI-CONSTRAINT)
 returns UI-CONSTRAINT-CLASS

----

(draw-constraint UI-CONSTRAINT)

(undraw-constraint UI-CONSTRAINT)

(draw-all-constraints)
  -> use the global list of UI-CONSTRAINTS in effect, if we choose that approach

(undraw-all-constraints)
  -> use the global list of UI-CONSTRAINTS in effect, if we choose that approach