code: private void setTag(final int i, final String name, final String value, 
        final boolean groupby) {
      setTagName(i, name);
      setTagValue(i, value);
      isTagGroupby(i, groupby);
    }
docs: Changes the name/value of an existing tag.
  @param i The index of the tag to change.
  @param name The new name of the tag.
  @param value The new value of the tag.
  Requires: {@code i < getNumTags()}.