Objects that implement the NSMutableCopying protocol will a new instance of the mutable version of the object. For example calling MutableCopy on an NSCharacterSet returns an NSMutableCharacterSet.

Types that implement the NSMutableCopying protocol include: MonoTouch.AVFoundation.AVAudioMix, MonoTouch.AVFoundation.AVAudioMixInputParameters, MonoTouch.AVFoundation.AVComposition, MonoTouch.AVFoundation.AVMetadataItem, MonoTouch.AVFoundation.AVVideoComposition, MonoTouch.AVFoundation.AVVideoCompositionInstruction, MonoTouch.AVFoundation.AVVideoCompositionLayerInstruction, MonoTouch.Foundation.NSArray, MonoTouch.Foundation.NSAttributedString, MonoTouch.Foundation.NSCharacterSet, MonoTouch.Foundation.NSData, MonoTouch.Foundation.NSDictionary, MonoTouch.Foundation.NSIndexSet, MonoTouch.Foundation.NSObject, MonoTouch.Foundation.NSSet, MonoTouch.Foundation.NSString, MonoTouch.Foundation.NSUrlRequest, MonoTouch.StoreKit.SKPayment and MonoTouch.UIKit.NSParagraphStyle.