The property inspector

The Property Inspector allows you to set some common properties for UI elements, such as alignment, position and size as well as specific settings for certain UI elements (selection state, text properties, color, etc.).

You can toggle the Property Inspector with the keyboard shortcut CTRL/⌘+; or ALT/OPTION+ENTER. When hidden you can also toggle it by right-clicking a UI element and selecting "Properties...".

If you have multiple UI elements selected it will display properties that are common to all the selected UI elements, as well as options for aligning and distributing the selection.

When no UI elements are selected, the Property Inspector shows notes for the selected wireframe.

For Components, it also shows the count and name of wireframes where the selected object is used.