System Coercion Table
The system coercion table is a table in the system heap that contains
coercion handlers that are available to all applications and processes running
on the same computer. The handlers in your application's coercion table are
attempting to coerce data, it first looks for a coercion handler in your
application's coercion table. If it cannot find a handler for the
descriptor type, it looks in the system coercion table for a handler. If it
doesn't find a handler there either, it returns the errAEHandlerNotFound
result code.
If you add a handler to the system coercion table, the handler that you specify
must reside in the system heap. If there was already an entry in the system
coercion table for the same descriptor type, it is replaced. Therefore, if there
is an entry in the system coercion table for the same descriptor type, you
should chain it to your system handler.
Note: When an application calls a system coercion handler, the
A5 register is set up for the calling application. For this reason, if you
provide a system coercion handler, it should never use A5 global variables or
anything that depends on a particular context; otherwise, the application that
calls the system coercion handler may crash.