XML was designed to store and transport data. It is the Extensible Markup Language that improves the functionality of the Web by letting you identify your information in a more accurate, flexible, and adaptable way.
When Linnworks downloads an order, it downloads the information into XML format. You can see this raw data yourself by right-click > View > View Order XML.
XML is stored in Linnworks for 30 days after the order is processed. For the open order, XML will always be present.