How to use NSAccessibilityCustomAction?

The NSAccessibility section of the High Sierra AppKit Release Notes say "To see an implementation of using NSAccessibilityCustomAction, please check out the developer sample code project AccessibilityUIExamples." But even the latest version 3.0 of the AccessibilityUIExamples sample code released about a month ago does not implement NSAccessibilityCustomAction. Is this available somewhere else, or will it be included in an update to the sample code?