I am confused reading the spec for purl in relation to golang sub-modules.
For example, looking at the submodule expressed in this go.mod file: https://github.com/go-modules-by-example/submodules/blob/master/a/go.mod, released by the a/v1.0.0 tag: https://github.com/go-modules-by-example/submodules/releases

Is the purl:

1. pkg:golang/github.com/go-modules-by-example/submodules/a@v1.0.0
2. pkg:golang/github.com/go-modules-by-example%2Fsubmodules%2Fa@v1.0.0
3. pkg:golang/github.com/go-modules-by-example@v1.0.0#submodule/a
4. pkg:golang/github.com/go-modules-by-example/submodule@v1.0.0#a
5. pkg:golang/github.com%2Fgo-modules-by-example%2Fsubmodules%2Fa@v1.0.0

It basically comes down to what is the namespace (if any), what is the name and what is the sub-path (if any) for this submodule.