A standard MIDI file consists of several data chunks. Each chunk has an identifier which specifies the type of data in the chunk, e.g., MThd and MTrk. The identifiers are four characters long.
A style file is a standard MIDI file with conventional MIDI chunks and Yamaha proprietary chunks. One of these proprietary chunks is the CASM chunk.
CASM is the four character identifier for the chunk containing chord transpositin data such as the NTTs and NTRs, chord note, chord type, etc. A CASM editor modifies the CASM chunk.
-- pj