@only / @except

@only and @except restrict which kinds (or fields) a slot accepts. @only is an include-list — nothing outside it is allowed — while @except is an exclude-list that admits everything else.

@block("layout") type Layout {
  @only("header", "footer")
  @children("section") fixed: list<Section>

  @except("draft")
  @children("section") published: list<Section>
}