You may want to designate an application-defined function in conjunction with a key filter function to ensure that editable text is valid in cases such as a cut, paste, or clear, where a key filter cannot be called. Such a function has the following type definition:
typedef pascal void (ControlEditTextValidationProcPtr) (ControlHandle control);
See
MyControlEditTextValidationProc
for more information about how to implement the application-defined function.