It's the extensible nature of XML that gives it an advantage. You can add custom elements and attributes whilst conforming to the base schema.
Granted, XML isn't the only format where this is possible. You can sort of achieve it with JSON, though XML's namespace system helps deal with name collisions. Adding bank-specific messages wouldn't be possible (or would be difficult) with fixed-column formats, for example, unless they had been specifically designed to be extended.
Granted, XML isn't the only format where this is possible. You can sort of achieve it with JSON, though XML's namespace system helps deal with name collisions. Adding bank-specific messages wouldn't be possible (or would be difficult) with fixed-column formats, for example, unless they had been specifically designed to be extended.