The diagram a layer says it is (MaidrLayer.diagramType), when MAIDR knows it. Guarded rather than trusted, as a title is, because a producer's JSON can carry anything.
Optional
The layer, when there is one
The diagram type, or undefined when the layer names none MAIDR knows
The diagram a layer says it is (MaidrLayer.diagramType), when MAIDR knows it. Guarded rather than trusted, as a title is, because a producer's JSON can carry anything.