AnnotationSpec

AnnotationSpec = { at: Value; channel: "x" | "y"; kind: "line"; label?: string; } | { channel: "x" | "y"; from: Value; kind: "band"; label?: string; to: Value; } | { kind: "point"; label?: string; x: Value; y: Value; } | { kind: "text"; text: string; x: Value; y: Value; }

Defined in: spec/annotation.ts:10

A reference mark that comes from the caller rather than from the data: a budget line, a target band, a highlighted point, a labelled event.

Every real chart eventually needs “the threshold is here”, and expressing it as a second data frame would misrepresent an assertion as an observation.