An Onion Skin toolbar has been added to A:M so that you don't have to return to the Options>Onion Skin panel whenever you need to change the most commonly used settings.
To enable the Onion Skin Toolbar go to Tools>Customize>Toolbars and check "Onion Skin"
The Toolbar has five controls
Onion Skin Mode ON/OFF (default keyboard shortcut: SHIFT+5)
Keyframe Mode ON/OFF. ON shows only onion skins at the time of keyframes of the currently selected object*&^. OFF shows onion skins in normal time increments (every frame if Step is set to 1) (a keyboard shortcut for this can be defined in Tools>Customize>Keyboard "Onion Toggle Mode")
increase/decrease onion skins drawn Before current time.
increase/decrease onion skins drawn After current time
increase/decrease Step. Step is an increment between drawn onion skins. Larger numbers skip more frames before drawing another onion skin
Like all toolbars, Onion Skin can be dragged to any convenient location.
In this view, with Keyframe Mode ON, A:M draws one keyframed pose of the character before the current time and two keyframed poses after. (The model with the white wireframe lines is at the current time)
With Keyframe Mode OFF Onion Skin draws in regular frame increments, observing the specified limits of one before and two after...
In this view, Step has been increased to 4. A:M draws onion skins in 4-frame increments...
Note that keyframe filters have an effect on what A:M regards as a keyframe for this purpose. If you had only the "Key Rotation" filter enabled while Onion skin was ON and in Keyframe Mode, it would only consider keyframes that contained Rotation keys for drawing onion skins and ignore any that had only Translation or Scaling keys.