HierarchyControl draws a structure top-down: a whole and its parts, each part a box with a title and a subtitle, joined to its parent by an elbow connector. A deal → its options → what each option covers; a programme → its layers; an organisation → its units. Never draw this as hand-built SVG in Controls.Html — compose the control.

Controls.Hierarchy(
    new HierarchyNode("deal", null, "MTPL 2026", "Submission · 2 options", "Acme/MTPL2026", HierarchyEmphasis.Strong),
    new HierarchyNode("o1", "deal", "Layer 1", "7m xs 3m · 7.8% RoL", "Acme/MTPL2026/Layer1", HierarchyEmphasis.Current),
    new HierarchyNode("o2", "deal", "Layer 2", "15m xs 10m · 3.1% RoL", "Acme/MTPL2026/Layer2"),
    new HierarchyNode("s1", "o1", "Motor", "Section", "Acme/Sections/Motor"),
    new HierarchyNode("s2", "o1", "Liability", "Section", "Acme/Sections/Liability", HierarchyEmphasis.Muted))

Nodes are FLAT

Each HierarchyNode(Id, Parent, Title, Subtitle?, Href?, Emphasis?) names its parent by id — the shape a projection produces naturally, and one that crosses the wire without recursion. The tree is resolved by the pure, unit-tested HierarchyControl.Layout(nodes) (FigureControlsTest):

a node whose parent is blank, itself, or not among the nodes is a root;
children keep their input order;
a repeated id keeps its first occurrence;
a cycle is broken at its first node in input order, so every node is drawn exactly once and no renderer recurses forever.

It returns null for no nodes, and the view says "No structure to show." in the viewer's language.

A deal of options and layers, and chained covers

Beyond the six positional fields a node carries init-only slots for the shapes deals actually take:

Slot	Vocabulary	Use
`Kind`	`HierarchyNodeKind`: `group`, `option`, `proportional`, `excess-of-loss`, `section` (open)	styles the box — a quota share and an XL layer must not look alike
`Relation`	free text, localized	the edge label to the parent — "option", "inures to", "on retention of"
`Arrange`	`HierarchyArrangement`: `row` (default), `stack` (open)	how the node's CHILDREN lay out; `stack` draws them one above the other, a tower (give the highest layer first)
`Badges`	short localized strings	status chips — a verdict, "bound", "★ favourite"
`Figures`	`KpiItem(Label, Value)`	small figures on the box — our line, our premium

So the general deal — a submission → 2–5 mutually exclusive options (one favourite) → each option's 1–6 layers → what each layer covers — stays readable: the options sit side by side, each option stacks its layers into a column, and a layer's sections sit under it.

Controls.Hierarchy(
    new HierarchyNode("qs", null, "Quota share 50 %", "30 % commission")
        { Kind = HierarchyNodeKind.Proportional, Arrange = HierarchyArrangement.Stack },
    new HierarchyNode("xl2", "qs", "XL layer 2", "10m xs 10m · 2.4 % RoL")
        { Kind = HierarchyNodeKind.ExcessOfLoss, Relation = "on retention of" },
    new HierarchyNode("xl1", "qs", "XL layer 1", "5m xs 5m · 6.1 % RoL")
        { Kind = HierarchyNodeKind.ExcessOfLoss, Relation = "on retention of",
          Figures = [new KpiItem("Our premium", "77.5k")], Badges = ["bound"] })

Emphasis and links

Emphasis is an open vocabulary (HierarchyEmphasis): current — the node the page is about, outlined in the accent colour and never a link; strong — the heading node, filled in the accent colour; muted — a node of secondary weight; favourite — the preferred alternative, marked with a star; empty — an ordinary box. Every other node with an Href is a link; HierarchyControl.LinkOf(node) decides. It normalises a bare mesh path to a site-root-relative one and accepts absolute http/https URLs. Any other scheme (javascript:, data:, …), a protocol-relative //host, and any href carrying a backslash or a control character (browsers normalise both into //host) draw the box unlinked, because node content is authored by people and a bound href must never become script. The favourite's star carries a localized accessible name, so it is not conveyed by colour and glyph alone.

Binding

Nodes is object: hand the rows over directly, or bind them to a live data section with a JsonPointerReference (Data Binding). AnalysisRows.Resolve<HierarchyNode> reads both forms. The Blazor renderer ships in the analysis view pack (MeshWeaver.Blazor.Analysis, AddAnalysisViews) and is drawn with CSS boxes and connectors, so it follows the theme and every label stays selectable text.