anchor.diff:  -H "Content-Type: application/json" \
   -d '{
     "event" : "$set",
  -  "entityType" : "item"
  +  "entityType" : "item",
     "entityId" : "i0",
     "properties" : {
       "categories" : ["c1", "c2"]
  
positive.code: -H "Content-Type: application/json" \
  -d '{
    "event" : "view",
    "entityType" : "user"
    "entityId" : "u0",
    "targetEntityType" : "item",
    "targetEntityId" : "i0",
  
negative.code: -H "Content-Type: application/json" \
  -d '{
    "event" : "$set",
    "entityType" : "user",
    "entityId" : "u0",
    "eventTime" : "2014-11-02T09:39:45.618-08:00"
  }'
  