sets...

[Vijay Saraswat <vj@research.att.com>]

    <DT> MCP Messages
    <DD> An <EM>MCP message</EM> is a parsed network message; it consists
    of a <EM>message name</EM>, indicating an action to be taken, an
    <EM>authentication key</EM>, and a set of keyword-value pairs, which
    supply arguments to the message.  This document uses the word
    "message" to refer to MCP messages.
 
Do you want to permit {a:1, a:3}? Thats a set of keyword-value
pairs.