Read about style format differences and how to convert between models at Style File Features.
The MIDI section can be created and edited in sequencer software. Read more here.
The Yamaha keyboard styles are MIDI format 0 files. The internal structure of the style file can be viewed in any MIDI program that supports Text Markers (e.g. Cakewalk, Cubase, WinJammer).
The MIDI section is divided in style parts with Text Markers (a normal MIDI "tag"), which defines where the MIDI data for this particular style part (e.g. "Main A") begins. Each style part matches the keyboard model features. Normally keyboards can use all style files even though they may have fewer or more style parts.
The first measure holds voice definitions, volume, reverb, chorus, pan etc. settings. The following measures hold the accompaniment patterns.
If you change the extension of a style file to "mid", you can open it and listen to it with any MIDI player though it may sound strange.
Don't save a style file in sequencer software. The above mentioned additional sections will be lost.