They are intended to address use cases like input-method writing solutions based on iink SDK, where your application performs the strokes capture and rendering.
They simplify iink SDK integration when the ink is simply an input medium for digital content.
The Gesture recognizer is dedicated to the recognition of gestures without any text context. It is agnostic to the current language settings.
The Text recognizer enables the recognition of text in incremental mode.
The Math recognizer enables the recognition of math.
The Shape recognizer enables the recognition of shapes in incremental mode. It is dedicated to the recognition of shapes only: no matter which ink content is sent to the Shape recognizer, it returns the shape(s) that it recognizes, with alternative recognized shape(s), if any.
In incremental mode, Recognizers process the first strokes in the background while the user keeps writing more strokes. That background recognition process starts as soon as the first stroke is written.