text: format and reference management system commonly used in conjunction with LaTeX typesetting. It serves as a way to organize and store bibliographic information for academic and research documents.BibTeX files have a .bib extension and consist of plain text entries representing references to various publications, such as books, articles, conference papers, theses, and more. Each BibTeX entry follows a specific structure and contains fields for different bibliographic details like author names, publication title, journal or book title, year of publication, page numbers, and more.Bibtex files can also store the path to documents, such as .pdf files that can be retrieved.Installationâ€‹First, you need to install bibtexparser and PyMuPDF.#!pip install bibtexparser pymupdfExamplesâ€‹BibtexLoader has these arguments:file_path: the path the the .bib bibtex fileoptional max_docs: default=None, i.e. not limit. Use it to limit number of retrieved documents.optional max_content_chars: default=4000. Use it to limit the number of characters in a single document.optional load_extra_meta: default=False. By default only the most important fields from the bibtex entries: Published (publication year), Title, Authors, Summary, Journal, Keywords, and URL. If True, it will also try to load return entry_id, note, doi, and links fields. optional file_pattern: default=r'[^:]+\.pdf'. Regex pattern to find files in the file entry. Default pattern supports Zotero flavour bibtex style and bare file path.from langchain.document_loaders import BibtexLoader# Create a dummy bibtex file and download a pdf.import urllib.requesturllib.request.urlretrieve(    "https://www.fourmilab.ch/etexts/einstein/specrel/specrel.pdf", "einstein1905.pdf")bibtex_text = """