XML, not just a good idea.
I thought this silver bullet was supposed to make this sort of thing magically go away? At the small price of completely bloating the data and forcing everything under the sun in the same hierarchical format, because hierarchies fit everything, moreso if you whip up a schema to go with it, and hey, there's standard tools to check all the < and > aren't mismatched, for that extra robustness. Yet all those standards and tools that were sold as solutions for all your input validation problems didn't protect from this. Who's misplaced the pixie dust then?