A type-string slot gains the ? marker it already understands. Every other
slot kind — a validator, an array, a nested schema — has no marker of its
own in the schema language, so it becomes a validator that also accepts
undefined, which Infer reads as an optional key just the same.
One schema slot, made optional.
A type-string slot gains the
?marker it already understands. Every other slot kind — a validator, an array, a nested schema — has no marker of its own in the schema language, so it becomes a validator that also acceptsundefined, whichInferreads as an optional key just the same.