langchain/document_loaders/parsers/registry.py/_get_default_parser
def _get_default_parser() -> BaseBlobParser:
    """Get default mime-type based parser."""
    return MimeTypeBasedParser(
        handlers={
            "application/pdf": PyMuPDFParser(),
            "text/plain": TextParser(),
        },
        fallback_parser=None,
    )