It's also something of a legacy convention (though one I prefer to maintain), from when PDF files were a leading vector for malware.
Though even back then, malware concerns aside, people would curse when a link caused Acrobat Reader (or, depending on one's system, the full Acrobat program) to unexpectedly fire up. Once upon a time, browsers didn't have integrated PDF handling.
And, even now, with integrated PDF handling, said handling is not proof against exploits.
It's a hint on corrodes built-in functionality and extensibility. It not only provides a way of parsing, but also a way of validating the parsed data via asserts.
> It's a hint on corrodes built-in functionality and extensibility.
Well, OK, but it was completely lost on me. One thing that did occur to me is that using the words "corrode" and "batteries" together might not evoke positive feelings in the mind of potential users.
[1] https://www.netlify.com/blog/how-we-run-nextjs/