Look up a rating split by key (e.g. 'overall-open',
'singles-12-13', 'gender-40+'). Returns undefined if the
player has no rating for that bracket.
Whether the player has a rating for the given split key.
All split keys the player has ratings for.
All rating splits the player has.
[key, split] pairs for every rating split.
for (const [key, split] of sportRating) { ... } — iterate every
rating split the player has in this sport.
A player's ratings for a single sport.
The top-level
rating/abbris the primary rating for that sport (conventionally the overall-open bracket). Every category × age bracket the player has played is also available via get, has, subscript-style access, and iteration.