I note the entry for the Origin parameter reads: 'The Origin is the center of the scale.' This is not a well formed sentence, and seems confused. ~~ugajin 31 October 2016
It may help to include a note for users who may be looking for a scale primitive to be directed to the Stretch primitive. ~~ugajin 31 October 2016
Re: ' In versions prior to 0.63.05 Scale Layer was called "Zoom layer".'. I feel re-naming 'Zoom Layer' as 'Scale Layer' was probably a mistake, and that the change ought to be reversed. Naming it 'Scale Layer' brings certain expectations about what it does, and how the primitive ought to behave, and give rise to confusion. Any expectations may be better met if the primitive is named 'Zoom Layer'.
The Stretch primitive appears to operate more like a scale operation than Scale Layer. Stretch, may also be wrongly located in the Distortions sub-menu. However, relocating and/or re-naming Stretch e.g. as Scale and placing it in the Transform menu is probably not a good idea unless Scale Layer is e.g. re-named Zoom Layer.
The Stretch primitive, both stretches and compresses content, and appears to behave as a 'Scale' layer would do. The user can scale content both x and/or y axes independently, and define a unit value. However, assuming one wanted to do so, it cannot easily be named Scale, if that name is already taken. ~~ugajin 31 October 2016