Length

Contains the size of this structure, in bytes, including Length itself. Valid Length values are 8, 12, and 24. Length values of 8 and 12 are used for notifications pertaining to session information, such as session creation, termination, saving/restoring of sessions, and session switching. A length value of 24 is used for Alternate Input Methods (AIM) value verifications and activations. Notifications received with Length values other than those defined above should be returned with an ERROR_INVALID_PARAMETER error code.