code: protected void appendInputTag(String tag) {
          final TagView previousInputTag = getInputTag();
          if (previousInputTag != null) {
              throw new IllegalStateException("Already has a INPUT tag in group.");
          }
  
          final TagView newInputTag = new TagView(getContext(), TagView.STATE_INPUT, tag);
          newInputTag.setOnClickListener(mInternalTagClickListener);
          addView(newInputTag);
      }
docs: Append a INPUT tag to this group. It will throw an exception if there has a previous INPUT tag.
  
  @param tag the tag text.