code: public boolean setEnabled(String label, boolean enabled) {
          return enabled ? labels.contains(label) && disabled.remove(label)
                         : labels.contains(label) && disabled.add(label);
      }
docs: Set whether an abbreviation is enabled or disabled.
  
  @param label   the label (e.g. Ph, Et, Me, OAc, etc.)
  @param enabled flag the label as enabled or disabled
  @return the label state was modified