ONSOURCE
ONSOURCE returns a character string whose value is the contents of the field that was being processed when the CONVERSION condition was raised.
It is in context in an ON-unit (or any of its dynamic descendants)
for the CONVERSION condition or for the ERROR or FINISH condition
raised as the implicit action for a CONVERSION condition.
If ONSOURCE is used out of context, a null string is returned.
If the source in a failed conversion is a COMPLEX value, then ONSOURCE() will show only the REAL or IMAG half of that value.