docs: public void constraintSouth(JComponent target, JComponent top, JComponent bottom, int padV ) {
          if( bottom == null ) {
              layout.putConstraint(SpringLayout.SOUTH, target, -padV, SpringLayout.SOUTH, this);
          } else {
              Spring a = Spring.sum(Spring.constant(-padV),layout.getConstraint(SpringLayout.NORTH,bottom));
              Spring b;
              if( top == null )
                  b = Spring.sum(Spring.height(target),layout.getConstraint(SpringLayout.NORTH,this));
              else
                  b = Spring.sum(Spring.height(target),layout.getConstraint(SpringLayout.SOUTH,top));
  
              layout.getConstraints(target).setConstraint(SpringLayout.SOUTH, Spring.max(a,b));
          }
      }