From VFXPedia

Controls List

Click on the small arrow button to the far right of the label for a popup list of the onscreen controls for the selected tools. The currently active control is marked on the menu. Choosing a different control from the menu will activate it for use. This can be handy when several controls are in the exact same position.

If multiple tools are selected, the menu will provide a complete list of all of their onscreen controls. Selecting a control from the list will highlight and activate this control on the view.

Shortcut: Pressing Tab or Shift+Tab will cycle through the onscreen controls, activating each in turn.

See Also: The view's context menu has further options for control management in the Controls submenu.