This article is from the Mac Programming FAQ, by Jon Watte email@example.com with numerous contributions by others.
All the HXxx calls that take a vRefNum and parID as well as the file
name are implemented in glue that works on any system that has HFS
(meaning 3.2 and up with the HD20 INIT, and all systems from System 6
The glue is available in MPW 3.2 and up, and Think C 5.0 and up. This
goes for all HXxx calls except HOpenDF; therefore, if you are interested
in System 6 compatibility, use HOpen instead and make sure you don't
allow file names beginning with a period.