Form calls the user edit routine with the type parameter equal
to U_CANCEL when the CANCEL key sequence is pushed. The other parameters
are NULL. U_CANCEL means that the user wishes to cancel the current
operation. The user edit routine can inspect the current record using the sread
function and decide if the cancel should be allowed. If the user edit routine
returns an error message, the cancel is not allowed. The cancel function is
meant as a safety valve for users who get stuck. Unless there are serious problems
with allowing a cancel, the user edit routine should always return NULL
from this call.
If an UPDATE is canceled, the user edit routine is first called with the type parameter set to U_CANCEL. Then each field on the form is updated to its original contents, and finally, the user edit routine is called with the with the same sequence of U_PREPARE and U_STORED calls as if the user pressed the STORE key.
If an ADD is canceled, the user edit routine is first called with the type parameter set to U_CANCEL. Then each field on the form is cleared, calling the user edit routine as necessary.