Aggregations in viz control

The api documentation says for FeedItem:

new sap.viz.ui5.controls.common.feeds.FeedItem(sId?, mSettings?)

The supported settings are:

• Properties
  • uid : string
  • type : string
  • values : string[]
• Aggregations
• Associations
• Events

What are the possible values for Aggregations here?

I tried this without success.

var feedValueAxis = new sap.viz.ui5.controls.common.feeds.FeedItem({

                'uid': "valueAxis",

                'type': "Measure",

                'values': ["Positive"]

            },

            "sum"),

Has anyone used this property?

Thanks for the help,

Regards,

Ashik