All marks are trademarks of ForexFeed. Skip to high content. Technical Documentation Data API API Docs Java Data API PHP Data API Close Data API dotNet Data API Open Service Data Retrieval Data Formats JSON XML CSV. XML Data Feed Specifications. Extensible Markup Language XML is a markup language that defines a set of rules for encoding information in a format that is both human-readable and machine-readable. Many programming languages or application programming interfaces Data have been developed for software developers to use to process XML data.