Slovak license plate: Trailer (documented since 1997)

Format, years and the law

Format: LL 999YL, for example XI 264YX (L is any letter, 9 any digit)
The format above follows the issuing rules: a registration that fits it is one this series could have issued.
Years issued: Documented since 1997; the format is likely older than the first year documented. Still issued.
Vehicle class: Trailer: trailers and semi-trailers where separately serialized. Issued for trailer and semitrailer.
Colours: Characters #000000 Background #FFFFFF
Size: 520 × 110 mm · every country's size

Trailer 340×200 mm

trailer · 340 × 200 mm

Trailer 240×150 mm

trailer · 240 × 150 mm
Region code notes: For plates issued before 1 January 2023 the leading pair is the district, as on any Slovak plate of that era; for later ones it is not. The Y is unaffected by the reform, it is a VEHICLE-CATEGORY marker, not a geographic one, and it is the only positional meaning in the Slovak serial that 2023 left standing.

vyhláška č. 9/2009 Z. z. § 35 ods. 2, 3, 4 and 11 písm. a). https://www.slov-lex.sk/static/pdf/2009/9/ZZ_2009_9_20230101.pdf

The series id is sk-trailer. The API returns its format, validation, colours and designs with the rest of Slovakia's series:

curl -s https://vehiclesdb.com/api/v1/plates/sk \
  -H "Authorization: Bearer $VEHICLESDB_API_KEY" \
  | jq '.series[] | select(.id == "sk-trailer")'