MDLscore is a text file format describing the MIDI file associated with a musical score.
This application allows composers, through this format, to create and modify MIDI files to specify execution dynamics such as tempo, sound level, tempo and sound variations, musical instrument change within the score, musical sequence repeats, control of the synthesizer (reverb, vibrato, etc.).
The MDLscore file can be created manually with a text editor, but is mainly intended to be generated automatically by the application, from a standard MusicXML file produced by music score editors (such as the MuseScore free editor for example).
See this site for a complete description : http://www.mdlscore.com/