Mac OS X has a 'zoom' action which can be used in various views in applications e.g. Photos.app when looking at a photo, zooming an entire Safari page, zooming in an NSScrollView.
This action is easily performed on a trackpad by using the 'pinch' gesture.
I cannot for the life of me, work out how to enable it for the Magic Mouse (when running Mac OS X 10.10 Yosemite).
The closest that I can get is in the 'Zoom' section of the 'Accessibility' pref pane. This allows you to zoom the entire screen which is not the behaviour that I'm looking for.
You used to be able to perform the zoom action using the mouse (see this video at 1:26 - https://youtu.be/UXbwOIsXNL8?t=1m26s )
So - have Apple removed this feature? Or is there a way to enable in-app zooming with the Magic Mouse?