The ISO 217:2013 standard defines the RA and SRA paper formats.
RA stands for "raw format A" and SRA stands for "supplementary raw format A".
This allows bleed (ink to the edge) on printed material that will be later cut down to size.
These paper sheets will after printing and binding be cut to match the A format.
Paper in the RA and SRA series format is intended to have a
aspect ratio but the dimensions of the start format have been rounded to whole centimetres.