# File lib/xml/dom/core.rb, line 2344
      def substringData(start, count)
        if start < 0 || start > @value.length || count < 0
          raise DOMException.new(DOMException::INDEX_SIZE_ERR)
        end
        ## if the sum of start and count > length,
        ##  return all characters to the end of the value.
        @value[start, count]
      end