Symbolic constraints

Symbolic constraints make it possible to define the relations among components without referencing their attributes directly. The following symbolic constraints are available.

• Equality and inequality constraints. The equality constraint A==B says that A and B are the same and the inequality constraint A != B says that A and B are different. Here, A and B can be constants , attribute variables, or components, but the types of A and B must match each other.    

• Position constraints. Constraints in this group relate the positions of two components. The following constraints belong to this group.

     inside(O1,O2) outside(O1,O2)
     left(O1,O2)   right(O1,O2)
     above(O1,O2)  below(O1,O2)
  

  The constraint R(O1,O2) can be read as "O1 is R O2." For instance, inside(O1,O2) says that the component O1 is inside the component O2.              

• sameXXX(O1,O2). This enforces that the components O1 and O2 have the same value for the XXX attribute. We can replace sameXXX with one the following:

         sameX sameY sameCenterX sameCenterY sameRightX sameBottomY 
         sameLocation sameSize sameWidth sameHeight  sameColor 
         sameFont sameRow sameColumn