code: protected void registerHorizontalGroupAttributes() {
          addAttributeProcessor(new HorizontalGroupAlignmentLmlAttribute(), "groupAlign");
          addAttributeProcessor(new HorizontalGroupFillLmlAttribute(), "groupFill");
          addAttributeProcessor(new HorizontalGroupPaddingBottomLmlAttribute(), "groupPadBottom");
          addAttributeProcessor(new HorizontalGroupPaddingLeftLmlAttribute(), "groupPadLeft");
          addAttributeProcessor(new HorizontalGroupPaddingLmlAttribute(), "groupPad", "padding");
          addAttributeProcessor(new HorizontalGroupPaddingRightLmlAttribute(), "groupPadRight");
          addAttributeProcessor(new HorizontalGroupPaddingTopLmlAttribute(), "groupPadTop");
          addAttributeProcessor(new HorizontalGroupReverseLmlAttribute(), "reverse");
          addAttributeProcessor(new HorizontalGroupSpacingLmlAttribute(), "groupSpace", "spacing");
      }
docs: HorizontalGroup widget attributes.