code: public void setHorizontalAlignment(HorizontalAlignmentConstant align) {
  
          if (align.equals(HasHorizontalAlignment.ALIGN_CENTER)) {
              // ignore center alignment
              return;
          }
          m_button.setHorizontalAlignment(align);
          m_align = align;
      }
docs: This is the alignment of the text in reference to the checkbox, possible values are left or right.<p>
  
  @see com.google.gwt.user.client.ui.HasHorizontalAlignment#setHorizontalAlignment(com.google.gwt.user.client.ui.HasHorizontalAlignment.HorizontalAlignmentConstant)