code: function VaultValue(topic, index, mediaType) {
  	// mediaType is optional, and may be set on setData
  
  	this.operation = null; // null (no change), 'set', 'touch', 'delete'
  	this.readMisses = [];
  
  	this.topic = parseTopic(topic);
  	this.index = parseIndex(index);
  	this.expirationTime = undefined;
  	this.mediaType = mediaType || undefined;
  	this.didExist = undefined;
  	this.willExist = undefined;
  
  	this.data = undefined;
  	this.encoding = undefined;
  
  	// cache for all differently encoded versions of this.mediaType (holds only data)
  	this.encodings = {};
  
  	// data/encoding match the latest selected encoding
  	// all encoded versions however can be found in this.encodings[]
  
  	this.liveVersionUninit = undefined;
  	this.liveDiff = undefined;
  }
docs: topic: a category of data index: a pointer to a specific piece of data for a given topic (alt: "index")