code: public Packer setYTopRelative(final boolean how) {
          if (how == true) {
              gc.gridy = GridBagConstraints.RELATIVE;
          } else {
              gc.gridy = 0;
          }
          setConstraints(comp, gc);
          return this;
      }
docs: Add gridy=RELATIVE to the constraints for the current component if how ==
  true 0 it if false.