From Just Solve the File Format Problem
RIFF STYL is a RIFF wrapper that seems to specify a Mac and Windows font to use to render included TEXT content.
Looks to contain 3 chunk types:
MAC" Maybe which font to use on Mac to render text along with other unknown info
WIN" Maybe which font to use on Windows to render text along with other unknown info
TEXT" What text to output
Files begin with "
RIFF", and have "
STYL" at offset 8.