[arccy]

https://pkg.go.dev/errors#Is

> An error is considered to match a target if it is equal to that target or if it implements a method Is(error) bool such that Is(target) returns true.

by default errors.Is matches the exact error variable, but you can use it to match other errors as well.

[zarldev]

I stand corrected. Still you cannot implement an Is on a sentinel error and is only applicable to concrete error types. And if I'm using concrete types I'm going to us errors.As