As you could see from examples for updating records using WBSP, when new
values for database table fields are received, the engine will replace old
values with new ones. However in some cases there is a need to store new value
that is related to old one (e.g. increased by some value, decreased by some
value, etc.), or to delete field value completely by setting new value to empty
string (""). Some of these tasks can not be done at all (without these
prefixes), and those that can be done require a lot of work to accomplish.
Therefore WBSP has defined update prefixes, special values that should be
added at the beginning of the WBF_ form fields, before the actual value. The
prefixes are:
$WBNULL$
$WBP$
$WB-$
$WB/$
$WB*$
$WBA$
$WBR$