docs: public void addConstraint(Constraint constraint) {
          if ( ConstraintType.ALPHA.equals(constraint.getType())) {
              this.addAlphaConstraint( (AlphaNodeFieldConstraint) constraint );
          } else if ( ConstraintType.BETA.equals(constraint.getType())) {
              this.addBetaConstraint( (BetaNodeFieldConstraint) constraint );
          } else {
              throw new RuntimeException( "Constraint type MUST be known in advance.");
          }
      }