This article is from the Mac Programming FAQ, by Jon Watte firstname.lastname@example.org with numerous contributions by others.
Wake Up and Smell the Glue!
How often have you wished you could use that cool new ToolBox
call, but didn't want to make your application System 7
dependent? Well, it might be that you *could* in fact have used
the call. Several traps are implemented in glue, that is, much
of their functionality is linked into your application and thus
available even if you are running under an old System.
This list applies to MPW 3.2 and should also be valid for the
current version of Think C. If you find any inaccuracies, please
report them to me. (email@example.com)
FSOpen: Tries first OpenDF, then Open.
HOpenResFile: Full functionality emulated if trap not available
HCreateResFile: Full functionality emulated if trap not
FindFolder: Under System 6, understands the following values for
folderType and returns the System Folder for all of them:
SysEnvirons: Full functionality emulated if trap not available
NewGestalt: Returns an error if not implemented
ReplaceGestalt: Returns an error if not implemented
Gestalt: The following selectors are always implemented:
vers mach sysv proc fpu
qd kbd atlk ram lram