Updatetype

| { action: "set"; key: Segments; value: unknown } //
	| { action: "with"; key: Segments; value: ImmutableArray<unknown> } //
	| { action: "omit"; key: Segments; value: ImmutableArray<unknown> } //
	| { action: "sum"; key: Segments; value: number }

Type
`Segments`	Series of string segments with at least one segment (this is what you actually get back when you split a string).
`ImmutableArray`	Immutable array: an array that cannot be changed.

A single decoded update to a keyed property in an object.

Discriminated by action: "set", "with" (add array items), "omit" (remove array items), or "sum" (add to a number).