ConstantEnvelope

Used for holding a constant numeric value.

You can instantiate a ConstantEnvelope like this:

ConstantEnvelope(propertyType: Envelope.PropertyType, value: Number)

Or without a property, like this:

ConstantEnvelope(value: Number)

A nice extension property is defined for this, so to create a ConstantEnvelope with the value 3.5, you can just do: 3.5.envelope.