Questions about resolving internal references in profile

[galtm]

I have questions about the profile resolution spec, in the internalref section, where it says:
"If the object fetched cannot be found or is not a valid OSCAL object, the tool MUST cease processing and provide an error."

Questions

1. Does the object-not-found case apply when anything interferes with fetching an object? For instance, should <import href="#nonexistent"/> return an error if there is no <resource id="nonexistent">? What if there is such a <resource> element but it does not contain a suitable <rlink> element?
2. What should an implementation be checking in order to determine whether the object fetched is a valid OSCAL object? Does "valid OSCAL object" mean valid according to the appropriate schema for the file format?

Thanks!