Desk accessories function as they always have under previous system versions.
A correctly-written DA will function normally under system software 6.0.X. The
one exception is when desk accessories are called under MultiFinder.
Desk accessories are DRVR resources and do not have, nor are they, CODE
resources. They can exist in open files in the System Folder and be picked up
when the drivers are called by an application or the Finder for display in an
Apple menu. The Apple menu resides in the System ROMs, and the DA list is
created by an application or by the Finder.
A change that may affect a DA is the loading of desk accessories into the
System heap. Desk accessories expecting to load into a specific application
heap will not function under the new system software. In the cases of these
application-specific and application-dependent desk accessories, the DA will
not know which application heap called it (since there could be multiple
application heaps).
The System has been patched to allow desk accessories to function within an
application-like environment belonging to the System. The environment is called
DA Handler. The DA Handler is a level of the System that executes desk
accessories when called. This is to allow all desk accessories to come to the
foreground when a DA is selected, rather than having to select the application
the DA belongs to. This also allows the System to control the Apple menu,
allowing selection of applications as well as desk accessories.