$schema

Type: String (relative path)
Required: No

"$schema": "../.hmiframework/Schema/ControlDescription.Schema.json"

This property references the JSON schema that describes the structure of Description.json. The schema is in a special folder of the framework control project. It is provided and updated by the NuGet package Beckhoff.TwinCAT.HMI.Framework. Including the JSON schema enables Intellisense in Visual Studio for each property.