The way protobufs handles versioning (old software ignores unknown fields) is far superior and realistically everyone uses 64 bit fixed length sizes everywhere
The idea is so simple that any change would be a misfeature.
The magic means it’s possible to identify the file type. Maybe you’ll add a tool later that operates on multiple types of files.
The version means you can evolve the contents in non-backwards-compatible ways, while maintaining the ability to read/parse the old version.
It’s a pain in the ass to add a magic or version number later; there’s a reason why nearly every file format on the planet has both.
XML
JSON
YML
TOML
<?xml version="1.1" encoding="UTF-8" ?>
> they're not file formats
Brb, gonna delete all my files without file formats
If you’re going to use text-based serialization formats as your justification for the decision, however, I’d suggest you look into all the fun bugs, security issues, and weird edges cases that arise from parsers having to make a best guess at character encoding and file format when all you have to work with is the file extension, maybe a byte order mark, and heuristics over the file contents.
In general, I find adding versions to things allows for much more graceful future redesigns and that is, IMO, invaluable if you're concerned about longevity and are not confident in your ability to perfectly design something for the indefinite future.