Format of papers and references in 77 13-87:

M- monographs, C- collections, N- newspaper articles, J- journal articles, D- papers, R- reports, S- standards, P- patents; For files that do not belong to the above types, use the letter "z" to identify them.

You see, there are no legal documents in it. Generally speaking, the citation of legal provisions is not included in the references, but if it is necessary to explain, it can be indicated in a footnote, for example, Article 20, Item 20 of the General Principles of the Civil Law stipulates: "the content of the provisions" and so on.