protocol

A protocol prolongs, amends, supplements, or supersedes an existing instrument. It may contain details pertaining to the application of an agreement, an optional arrangement extending an obligatory convention, or a technical instrument as an annex to a general agreement. It may substitute for an agreement or…

…single instruments called convention, agreement, protocol, declaration, charter, covenant, pact, statute, final act, general act, and concordat (the usual designation for accords with the Holy See); finally there are less formal agreements consisting of two or more instruments, such as “exchange of notes” or “exchange of letters.”