Training is optional for a recognizer and the method of its implementation is up to the developer. Through training, a recognizer can consider the individual style and writing characteristics of different users when interpreting handwriting.

Training can be classified as either passive or active. However, the distinction usually pertains more to the application than to the recognizer. In passive training, the application quietly calls the recognizer's training functions whenever the user corrects a wrong guess. Correctly implemented, passive training helps ensure that the recognizer learns from its mistakes.

Active training takes place only when specifically requested by the user. A training window prompts the user for written samples, then the verified input is given to the recognizer to store in its database for that user. The recognizer can provide the active training support, though usually this task is left to an application. Microsoft usability studies have shown that users do not object to the time invested in active training.

The following table lists the functions that a recognizer with training capabilities can export. Only TrainHREC is used by version 2.0 Pen API. The other functions are obsolete in version 2.0 and should be included in a recognizer only if it is expected to work with older applications that work with a version 1.0 recognizer (see the Microsoft Pen Windows version 1.0 documentation for descriptions of these functions).

Passes a previous recognition result that may contain errors along with the required interpretation. The system calls this function in response to a call to TrainContext. This function applies only to training recognizers compatible with version 1.0 of the Pen API. It is superseded by the TrainHREC function.
Passes ink data and its required interpretation to the recognizer. The recognizer then stores the data and interpretation for future reference.
Passes a previous erroneous recognition result along with the correct interpretation. The system calls this function when the application calls TrainInk. TrainInkInternal is rendered obsolete by TrainHREC and is only for training recognizers compatible with version 1.0 of the Pen API.

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