Swift is exploring a cute idea for library transparency: you can distinguish between "this ABI is guaranteed to keep working" and "I want an extra layer of indirection so I can add to data structures without breaking downstream users".
https://forums.swift.org/t/pitch-library-evolution-for-stable-abis/23026
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I'm working on arity errors in Garden, my toy programming language.
Rather than just saying "expected 3, got 4 arguments", I'm trying to report where the extra argument is, or what extra argument was expected.
One cute feature of markdown I'd not noticed before: there's no syntax for images *without* a description (i.e. alt text).
https://spec.commonmark.org/0.31.2/#images
I'm a huge fan of Swift's 'Error Handling Rationale' design document: https://github.com/swiftlang/swift/blob/9315673c003875158852579bd1f33480cdec5461/docs/ErrorHandlingRationale.md#fundamentals
It carefully defines terminology and compares with other languages, so you can understand Swift's position and preference in the design space.