Clean labeled structures

What XML brings to the table

Mandatory structure XML's foundation requirement is clean structure. Every start tag must have an end tag, nesting must be clean, names must conform to a set of rules, etc. While XML doesn't require particular structures or particular amounts of structure, best practices for XML tend to ensure that information is marked up as atomically as seems appropriate.
Labels XML's structures come with labels - element and attribute names. While, again, there is no requirement that these labels be meaningful in any sense, most developers use them in such a way as to take advantage of the meaning they can provide.
Open formats It's possible to obfuscate document labels, but anyone can open the document and see the core structure. For the most part, obfuscated formats are frowned on by the XML community, and the text-based nature of XML makes that a difficult if not pointless task in any event.
Standardized Toolset Structure testing, transformation, tree representation, event representation, digital signature generation... XML comes with a diverse and growing tool set.