public extension PureYAML.Model {
    /// A source span for a value-tree node: a start and end ``SourcePosition``. A collection
    /// spans from its opening to its closing event; a scalar carries a start-anchored span
    /// (start equal to end), because the event stream records a scalar's start mark only.
    struct SourceRange: Equatable, Hashable, Sendable {
        public var start: SourcePosition
        public var end: SourcePosition

        public init(start: SourcePosition, end: SourcePosition) {
            self.start = start
            self.end = end
        }

        /// A zero-width span at a single position, used when only a point is known.
        public init(at position: SourcePosition) {
            start = position
            end = position
        }
    }
}