legal ground
The Supreme People's Court's nineteenth provisions on evidence in civil proceedings.
The parties shall classify and number the evidence materials submitted by them one by one, briefly explain the source, object and content of the evidence materials, sign and seal them, indicate the date of submission, and submit copies according to the number of the other parties.
When the people's court receives the evidential materials submitted by the parties, it shall issue a receipt indicating the name, number of copies, number of pages and time of receipt of the evidence, and the person in charge shall sign or seal it.