understand `godebug` at all.)

The defaults from the `go` and `godebug` lines apply to all main
packages that are built. For more fine-grained control,
starting in Go 1.21, a main package's source files
can include one or more `//go:debug` directives at the top of the file
(preceding the `package` statement).
The `godebug` lines in the previous example would be written:

	//go:debug default=go1.21