Records in a REGIONAL(1) data set are either actual records containing valid data or dummy records. A dummy record in a REGIONAL(1) data set is identified by the constant (8)'1'B in its first byte. Although such dummy records are inserted in the data set either when it is created or when a record is deleted, they are not ignored when the data set is read; your PL/I program must be prepared to recognize them. You can replace dummy records with valid data. Note that if you insert (8)'1'B in the first byte, the record can be lost if you copy the file onto a data set that has dummy records that are not retrieved.