The two function components a host mounts to show the Map beside its own list: map_region/1, where the StatifierBlocksMap hook draws the document, and description_region/1, which says in words what the selected block is, or what the document is when nothing is selected.

They live in the StatifierBlocks.Editor.* namespace because they name Phoenix, and that namespace is where ADR-0005 decision 1's compile guard lives. The editor draws no map and never mounts map_region/1 (ADR-0018). It does mount description_region/1, under its canvas, from its own document, view model, palette and selection (ADR-0005's Amendment of 2026-09-29 on the shell arrangement); see "In the editor" below.

What the host brings

The components keep no state. A host passes four things, and each stays the host's:

The map region

map_region/1 renders the element the hook is attached to, inside a region hidden from assistive technology (aria-hidden="true"): a reader of the host's list would otherwise meet every step twice. The element scrolls, and a browser makes a scroll box with nothing focusable in it a Tab stop of its own, so it carries tabindex="-1"; nothing else in the region takes focus.

The element carries what the hook reads, in the attributes it reads them from: the graph StatifierBlocks.Map.graph/2 answers as JSON in data-graph, with the selection marked in it; whether the page can edit in data-editable; the list's event names in data-select-event and data-insert-event; the element to scroll into view after an insert armed from the map in data-insert-reveal, when the host names one; and the description region's id, its hover layer's and its store's in data-info-region, data-info-hover and data-info-store, when the host names the region, which is what gives the map its hover. The drawing goes into a child marked data-map-canvas, which LiveView leaves alone (phx-update="ignore").

The description region

description_region/1 renders the region with aria-live="polite", so a selection made in the list is read out, under the id the host's list rows name with aria-describedby. Its content is rendered on the server: the selected block's StatifierBlocks.Map.Info description, or StatifierBlocks.Map.Info.idle/4 when nothing is selected. A block's author-written note leads, above the built-in text (ADR-0001's Amendment of 2026-09-28, clause 2g). It shows values and never controls. The region's accessible name is its aria-label, "Description" unless the host passes its own words in label.

Beside the region, and hidden, it renders the store the hook's hover reads: one child per element the map draws, data-describes naming the element's map id, holding the same markup the region shows for it. The store's id is the region's with -store after it, which is the id map_region/1 stamps when it is handed the region's.

Selection speaks, hover is silent

What the region announces changes on a selection and never on a hover. The server writes the region, and only on a render: a row selected in the list, or a block selected on the map, which arrives as the list's own event. A hover is drawn in the hover layer instead, an element beside the region and outside it, with the region's id and -hover after it: aria-hidden="true", hidden until the hook fills it, and left alone by LiveView (phx-update="ignore"). The two sit in one frame, sb-map__description-frame, and while the layer is shown the stylesheet stacks it over the region and makes the region transparent, so the visible text is the hovered element's while the region's own content, and its aria-live, stay as the server wrote them.

In the editor

StatifierBlocks.Editor renders description_region/1 under its canvas with map={false}, which says no map is mounted beside the region. The region then renders without its hover layer and without its store, which only the Map's hook reads, and the document's idle description leaves out its explanation, the paragraph on how to read the map; the name, the description, what starts it and the counts stay. A selected block's description is unchanged. The default, map={true}, renders the region exactly as a host's page has it.