macRes: Tools for reading Mac resource forks
Classic Mac OS files are made up of two parts - the “data fork” which contains the file contents proper, and the “resource fork” which contains a number of structured data items called “resources”. Some fonts, such as Mac “font suitcases” and Type 1 LWFN fonts, still use the resource fork for this kind of structured data, and so to read them, fontTools needs to have access to resource forks.
The Inside Macintosh volume More Macintosh Toolbox explains the structure of resource and data forks.