Diagram

A flow or architecture diagram, drawn out of the system's own parts.

The alternative it replaces is a fenced block of box-drawing characters — ┌──────┬──────┐ — which is a picture rendered in a font chosen for code. It inherits the code block's frame and scrollbar, so a diagram reads as terminal output; it cannot wrap, so on a phone it either overflows or is scaled to nothing; the box edges are text, so a screen reader reads the rules out loud; and none of it responds to the theme.

The other alternative is a diagramming library, which is several hundred kilobytes of layout engine, renders after hydration, and draws in its own palette. This is neither: hairline frames on the radius scale, mono labels, the muted step for anything supporting — so a diagram belongs to the page it sits on. It server-renders, because it is markup.

NESTING IS CONTAINMENT, which is what most architecture diagrams actually describe: this is inside that, and these two sit beside each other. Edges are for the sequence between siblings, not for arbitrary wiring — a diagram that needs arbitrary wiring is a diagram that wants a drawing, and this will not pretend otherwise.

It takes a spec rather than markup, so a fenced ```diagram block in an article and a hand-written figure on a page are one renderer and one look — and a wrong diagram is corrected by editing data.