This is a form field value prefix for removing text from fields of string types (text, memo, etc.). When WBSP engine receives a WBF_tablefieldname form field value with this prefix for database table field of string type, instead of replacing the old value with new one, it will search the existing value for value sent by form (all text after $wbr$ prefix) and if it founds it, remove it from the database field (so new value stored in the database is OldDatabaseTableFieldValue with removed all occurrences of NewFormValue)
Here's an example:
After running this example (and pressing the "Remove second edition" button), if text - second edition exists in field Title of updated record of table Titles, it will be removed. If the text does not exist (not found), the database field will not be changed.