XML is not like other data format languages. XML is language-like, it's like a typical programming language that comes directly as an abstract syntax tree (AST)

XML is not like other data format languages. XML is language-like, it's like a typical programming language that comes directly as an abstract syntax tree (AST), without the parsing step. No other data exchange formats are like that. Yet this is exactly what people need to conveniently describe things for machines. So it's not exactly a machine-to-machine exchange format, but human-to-machine and machine-to-human. E.g. one of area where XML shines are user interface notations. A screen may have a tab that has another tab that may show yet another screen; a menu may have a submenu, and (although not recommended) a sub-submenu and so on. A field or text may appear here and there. The two chief things here are ordering and composition. XML is very good at that. Not as good as a dedicated UI language, perhaps, but, being generic, it's much more pliable an easier to tinker with.