The ST::groupThatCreatedThisInstance is pretty useless for STGroupDir, and it's not easy to re-generate the original file URL, for template name, so a resolved file URL is required; this could be null for STGroupString. It's probably best to put the resolved file URL on CompiledST, give its use in STGroup::importTemplates(Token fileNameToken).
The ST::groupThatCreatedThisInstance is pretty useless for STGroupDir, and it's not easy to re-generate the original file URL, for template name, so a resolved file URL is required; this could be null for STGroupString. It's probably best to put the resolved file URL on CompiledST, give its use in STGroup::importTemplates(Token fileNameToken).