Groups of related messages in the Multimedia extensions are identified by a prefix in the message names. The following table summarizes groups of related messages and the prefixes for each group:
| MCI |
Media Control Interface command messages |
| MIM |
MIDI input callback messages |
| MMIOM |
Custom I/O procedure messages |
| MM_JOY |
Joystick window messages |
| MM_MCI |
Media Control Interface window messages |
| MM_MIM |
MIDI input window messages |
| MM_MOM |
MIDI output window messages |
| MM_WIM |
Waveform input window messages |
| MM_WOM |
Waveform output window messages |
| MOM |
MIDI output callback messages |
| WIM |
Waveform input callback messages |
| WOM |
Waveform output callback messages |