This feature is non standard because it has never been seen on a PropertyGrid. But does it mean it is useless ? No of course !! In certain circumstances, while listing a lot of related dynamic data in the grid, it can be very convenient to offer the multi-selection to the user to be able to perform a set of tasks on all the selected properties at the same time. Two selection modes are offered:
In both modes, SHIFT and CTRL keys act as usual to select the properties. CTRL+A selects all the properties, regarding the active selection mode.

In this example, you see properties that have been selected while in the "Same level" mode (under the checklists node).
A special notification has been added to let the PropertyGrid control which individual properties can be part of the selection. In the screenshot, the Aircraft property has been forbidden to be selected.
Practically in this sample, the user has just to press the Delete key to remove the items in the checklist. The developper can of course offer a contextual menu to act on the selected properties.