Instantiate TemplateGroupFile from URI expects local file path

[Brubning]

Loading a template group file using a URI (as below) is expecting a local file path and not a web address.

            var templateGroupFile = new TemplateGroupFile(
                templateGroupS3Uri,
                Encoding.Default,
                '$',
                '$');
            var mainTemplate = templateGroupFile.GetInstanceOf(mainTemplateName);

I store my .stg files in an AWS S3 bucket because local file storage is not always available. I thought that the URI parameter would allow remote URIs.

Could be that I'm missing something?