Workaround to prevent VO from accessing elements in presenting view displayed beneath dimmed overlay. Default container view ignores `-accessibilityViewIsModal`

MLPatchTransitionViewAccessibility.m

/**
 *  Workaround to prevent VO from accessing elements in presenting view beneath overlay.
 *
 *  @param transitionView UIPresentationController.containerView
 */
static void MLPatchTransitionViewAccessibility(id transitionView) {
    NSCParameterAssert(transitionView);
    
    static Class transitionViewClass;
    static Class mlTransitionViewClass;
    static dispatch_once_t onceToken;
    
    dispatch_once(&onceToken, ^{
        SEL accessibilityViewIsModalSelector = @selector(accessibilityViewIsModal);
        
        transitionViewClass = NSClassFromString([@[ @"UI", @"Transition", @"View" ] componentsJoinedByString:@""]);
        
        // Add subclass of UITransitionView
        Method originalMethod = class_getInstanceMethod(transitionViewClass, accessibilityViewIsModalSelector);
        
        if(!originalMethod) {
            MLCLog(@"MLPatchTransitionViewAccessibility", MLLogLevelWarning, @"Cannot get %@.%@", NSStringFromClass(transitionViewClass), NSStringFromSelector(accessibilityViewIsModalSelector));
            return;
        }
        
        const char *methodEncoding = method_getTypeEncoding(originalMethod);
        
        // implement -accessibilityViewIsModal that always returns YES.
        IMP impl = imp_implementationWithBlock(^BOOL {
            return YES;
        });
        
        mlTransitionViewClass = objc_allocateClassPair(transitionViewClass, "MLTransitionView", 0);
        
        if(mlTransitionViewClass) {
            class_addMethod(mlTransitionViewClass, accessibilityViewIsModalSelector, impl, methodEncoding);
            objc_registerClassPair(mlTransitionViewClass);
            
            MLCLog(@"MLPatchTransitionViewAccessibility", MLLogLevelVerbose, @"Register class pair %@: %@", NSStringFromClass(mlTransitionViewClass), NSStringFromClass(transitionViewClass));
        }
    });
    
    if([transitionView isKindOfClass:transitionViewClass]) {
        object_setClass(transitionView, mlTransitionViewClass);
    } else {
        MLCLog(@"MLPatchTransitionViewAccessibility", MLLogLevelWarning, @"Expected an instance of %@. Got %@", NSStringFromClass(transitionViewClass), NSStringFromClass([transitionViewClass class]));
    }
}