The information the Inspector displays depends on which objects are selected and their state at the time.
Inspector Panel Selector
The Inspector Panel selector is a bank of 5 buttons that allow switching between the various Inspector panels. Click on the buttons to flip between the panels.

The Inspector Panels
Below are images of each Inspector panel.

Inspector Concepts

When multiple dissimilar objects with conflicting attributes are selected, the Inspector sometimes cannot display anything. For example, the Shape panel displays differently for shapes and connections, so if you select both shapes and connections, the Shape panel will display nothing. As another example, the Attachments panel can only examine and edit one object at a time, so if you select multiple objects, it too will display nothing.
For example, to edit the Shape tool defaults:





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