Control Tooltip

Purpose: Control what is displayed in the tool tip

Background: I am developing a custom visual. I would like to be able to control the tool tip for this visual. In my capabilities.json file I defined a tool tip under dataRoles and dataviewmappings. 

What is the next step? I want my tooltip to only display values that the user drags into ToolTip. Does anyone have tips into updating the visual.ts file? 

capabilities.json  code: 
"displayName": "ToolTip",
"name": "ToolTip",
"kind": "Measure"
...
"ToolTip": { "max": 3 }