UITextInputStringTokenizer

If you want to take advantage of this base implementation, you should subclass this class and handle application-specific directions and granularities affected by layout. When you instantiate a class you must supply the document class that is adopting the UITextInput protocol for your application.

When you subclass UITextInputStringTokenizer, override all UITextInputTokenizer methods, calling the superclass implementation (super) when method parameters are not affected by layout. For example, the subclass needs a custom implementation of all methods for line granularity. For the left direction, it needs to decide whether left corresponds at a given position to forward or backward, and then call super passing in the storage direction (UITextStorageDirection).