function makeRecursiveXMLString(variable, link) {
      const format =
          '<ToReplace xmlns="urn:mpeg:dash:schema:mpd:2011" ' +
          'xmlns:xlink="http://www.w3.org/1999/xlink" variable="%(let)s">' +
          '<ToReplace xlink:href="%(link)s" xlink:actuate="onLoad" />' +
          '</ToReplace>';
      return sprintf(format, {'let': variable, 'link': link});
    }
Creates an XML string with an xlink link to another URL,
for use in testing recursive chains of xlink links.
@param {number} variable
@param {string} link
@return {string}
@private