Parsing of "Buddylist Overlay"

In _parseMessage, you will recieve a lot of data with the type buddylist_overlay. Sample msg:

{
  "seq": 50,
  "t": "msg",
  "u": 1234567890,
  "ms": [
    {
      "type": "buddylist_overlay",
      "overlay": {
        "1234567890": {
          "a": 2,
          "c": 4170,
          "s": "push",
          "vc": 74,
          "la": 1518985361
        }
      }
    }
  ]
}

The 'a' (activeness?) value appears in two (and maybe more?) states: 0 and 2, where 0 means offline and 2 means online. The 'la' (last active?) value indicates the timestamp

This can be used to know when users become online or when they go offline (in real time, compared to onChatTimestamp, which only recieves these updates once in a while).

If anybody can figure out what the c, s or vc values could mean, please let me know (!), otherwise I'll probably make another onX function at some point.