The dataset viewer
How the viewer reads splits and columns, and what the preview rows are.
Each dataset page has a viewer that pages through rows by split. The viewer reads the column schema from the card, so it can show types and label columns as chips.
In the preview, viewer rows are illustrative samples generated from the schema. Real rows stream from the files once downloads open at launch.
Splits
Name splits train, validation and test. Shard large splits so no single file goes over about 1.5 GB.