New Composition - add a new Composition to the Scene.
Pre-Compose - create a new Composition and add any selected Elements to it.
Set Composition to Playback Range - the Composition Start and End Frames will be set to the Playback Range.
Set Playback Range to [Selection/ Composition] - this menu item is dependent on selection:
Selection - set the Playback Range to the earliest and latest frame of any selected Elements.
Composition - if nothing is selected then set the Playback Range to the Composition's Start and End Frame.
Solo Selection in Viewport /Clear Viewport Soloing - this menu item is dependent on selection:
Solo Selection in Viewport - add any selected Elements to the Quicklist and set the mode to Filter Viewport. See Tags.
Clear Viewport Soloing - with nothing selected this command will deselect the Quicklist to remove all Viewport filtering. See Tags.
Clear Quicklist - remove all Elements from the Quicklist.
Set Transparent Background - set the Background alpha to 0.