docs: public String getButtonDesc()
      {
          if (this.getDisplayFieldDesc(this) == false)
              return null;    // Don't display a desc with this control
          if (this.getSeparateFieldDesc())
              return null;    // Field desc is already a separate control, don't display
          if (this.getConverter() != null)
              return this.getConverter().getFieldDesc();  // Or override and supply value
          return null;
      }