def document_style_by_name(name)
      root_object.document_styles.each do |style|
        return style if style.name == name
      end
      nil
    end
def document_style_by_name(name)
      root_object.document_styles.each do |style|
        return style if style.name == name
      end
      nil
    end
Return document style by its name
 @param name [String] name of style
 @return [DocumentStyle, nil]