Ready for implementation
If I select an item, Magnolia provides me with a preview of the item as well as the list of common actions applicable to it. I can also retrieve a list of all actions defined on the currently selected item if I choose to do so, but it's the common actions which are visible by default.
Magnolia also offers me additional information on the item if available and if this makes sense in the current context. I could get a list of users working on a page in a interface showing me the status of work items. Or I could get access to a page's history to check out the changes applied to it in the last 24 hours.
Description of desired behavior
The Actions sidebar is used in AdminCentral to show both the actions on and a preview of the currently selected item or items. It is usually shown on the right-hand border (left-hand border on RTL setups) and is divided into two main areas.
The upper part always contains the list of actions, but may also show additional information on the currently selected item. It is implemented using an Actions Rack, which uses a dedicated unit for handling the list of actions. Please thus refer to the corresponding page for detailed descriptions on behavior and available functionality of the upper part of the sidebar as well as on how notifications are shown.
The lower part of the sidebar is entirely reserved to the preview of the selected item. The preview may be minimized to make more room available for the rest of the sidebar.
The preview takes over the entire lower area of the sidebar, which is always bottom aligned. It may be collapsed to make more room available for the Actions Rack and thus for the list of actions possibly other units currently visible.
A click on the preview image shows a larger version of it in an overlay dialog, which may also present additional details on the selected item such as its file size or modification date. If a single item has been selected and the view it was selected in is a list, a tree or a grid, the overlay dialog also offers forward and backward buttons to jump to the next (lower) or previous (upper) item in that view. If multiple items were selected, these forward and backward buttons are restrained to move to the next or previous item of the selection.
Collapsing the Actions sidebar
The sidebar can be collapsed so it uses up less space. When collapsed, only icons for the common actions, copy&paste, undo/redo as well as an icon to show the preview in a popup window are visible. The preview of the sidebar actually collapses alongside the Action Rack and remains available: it shows the thumbnail on request in a popup window.
Care must be taken to ensure that changing from the expanded view of the sidebar to the collapsed one does not disorient and confuse the user. Use the animations to smoothen the transitions as defined for the Actions Rack and slide the preview up and down instead of abruptly opening and closing it.