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