How to use the qface.generator.FileSystem._parse_stream function in qface

def parse_document():
    stream = InputStream(document)
    return FileSystem._parse_stream(stream)

def _parse_document(document: Path, system: System = None, profile=EProfile.FULL):
        """Parses a document and returns the resulting domain system

        :param path: document path to parse
        :param system: system to be used (optional)
        """
        logger.debug('parse document: {0}'.format(document))
        stream = FileStream(str(document), encoding='utf-8')
        system = FileSystem._parse_stream(stream, system, document, profile)
        FileSystem.merge_annotations(system, document.stripext() + '.yaml')
        return system