ONCHAR returns a character(1) string containing the character that
caused the CONVERSION condition to be 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 the CONVERSION condition.
>>-ONCHAR-+----+----------------------------------------------->< '-()-'
If the ONCHAR built-in function is used out of context, a blank is returned.