In the past, DC 0H'0' was preferred for defining labels because any DS, even of zero length, would cause a new TXT card to be started in the object deck, making it larger than necessary. The value is no longer needed, so DC 0H is allowed.
If no alignment padding is required, DC 0H and DS 0H are equivalent, but if alignment padding is required (which would not occur within instructions) then DC 0H will pad with a zero byte and continue on the same object code TXT card, but DS 0H will simply start a new TXT card at the aligned location. Jonathan Scott, HLASM IBM Hursley, UK
