I have actually seen it in an XML file in the wild. Never quite understood why they did it. Anything they encoded into there, they could have just added a node for.
But it was an XML format that was widely used in a big company, so presumably somewhere someone wrote a shitty XML parser that can't deal with additional nodes. Or they were just scared of touching the existing structure, I don't know.

That's assuming people actually use a parser and don't build their own "parser" to read values manually.

And before anyone asks: Yes, I've known people who did exactly that and to this day I'm still traumatized by that discovery.

But yes, comments would've been nice.