Color Burn and Color Dodge in blend Modes please !

Why colorBurn and colorDodge are nor blend modes ?

Having them in composite effect only, I can’t just apply them to a vector fill.

I mean, doc says :

object.fill = compositePaint
object.fill.effect = “composite.colorBurn”
object.fill.alpha = 1

But compositePaint must be a mix of two images. What if I just have a rect shape and want to do :

rect.blendMode = “colorBurn” ?

Could you help ?