The AMSNAVMODE command turns on and off a mode that is referred to as the Design Navigation mode.
While the Design Navigation Mode is on, when you move the cursor through model space, each component the cursor moves over highlights (in model space as well as in the mechanical browser) and a tooltip displays the hierarchical structure of the component.
If the selection mode is set to bottom-up, when you move the mouse over a geometry, the part that the geometry belongs to highlights. If the selection mode is set to top-down, the highest level assembly that the geometry belongs to highlights. The tooltip, shows the hierarchical structure of the components that the geometry belongs to, in the form of a tree. As you move the cursor over the plus sign (+) icon, the branches of the tree expand. As each level expands, the component highlights in model space and in the mechanical browser. You can click a node of the tree in the tooltip to select the component and the perform operations on it using the right-click menu.
The tooltips can be made semitransparent by pressing the CTRL key or clicking the wheel button (available only on wheel mouse).
When the Structure workspace is active, the Design Navigation Mode can be turned on or off using the 
button on the Ribbon or by pressing CTRL-D.