For iOS, Accessibility values are one of the building blocks of how Accessibility works on the platform, along with traits, labels, hints, and showing/hiding elements. If you’re familiar with WCAG or web accessibility, accessibility values are the value part of WCAG 4.1.2: Name, Role, Value.
Values #Not every element in your view will have a value - in fact, most won’t. Any element that ‘contains’ some data, data that is not included in the element’s label requires an accessibility value to be set. If you’re using standard controls provided by Apple, these values will be set for you. But if you make something custom you must add a value where necessary, and if you’re extending a standard control, testing with VoiceOver is essential.