Feedback on "NumberSequenceKeypoint.Envelope"

The purpose of Envelope is not made clear here. What is the envelope variance for, and how is it used in different contexts? (ParticleEmitter, UIGradient)

Affected URL: https://create.roblox.com/docs/reference/engine/datatypes/NumberSequenceKeypoint#Envelope

Note: I know its purpose (at least when it comes to particles), but others may benefit from it listed there.