version 1 .

Definition = <union @variants [Variant ...]> / Simple .
Variant = [@label symbol @type Simple] .

Simple = Field / Record .
Record = <rec @fields [NamedField ...]> .
NamedField = [@name symbol @type Field] .

Field =
/ =unit
/ =any
/ =embedded
/ <array @element Field>
/ <set @element Field>
/ <map @key Field @value Field>
/ <ref @name schema.Ref>
/ schema.AtomKind
.