When naming a command structure, include the command in the structure name. Also include the device type, in order to differentiate customized structures from the structures defined for the core commands. An example is the following structure, used with the extension to the play command for animation devices:
typedef struct tagMCI_ANIM_PLAY_PARMS {
DWORD dwCallback;
DWORD dwFrom;
DWORD dwTo;
DWORD dwSpeed;
} MCI_ANIM_PLAY_PARMS;