---
status: historical
created: 2026-09-29
archived: 2026-10-15
reason: "Superseded design; a room offers no message windows to anchor."
---

# ChatWindowAnchor

Where a window of messages sits in its view of the conversation. A client passes
one to a message list's `openWindow` (see
[`ChatMessageList`](../../../specs/fabrichat/ChatMessageList.md#windows)), as `from`.

```ts
// Shown for illustration only.
type ChatWindowAnchor =
  | { before: FabricEpochNsec | "end" }
  | { after: FabricEpochNsec | "start" }
  | { around: FabricEpochNsec };
```

Exactly one of the three keys is present.

## The anchors

- **`{ before: t }`**: the newest messages sent before `t`. With `"end"`, the
  newest messages there are. A client opening a conversation at its latest
  messages uses `{ before: "end" }`, and pages back with `{ before: t }`, where
  `t` is the `sentAt` of the oldest message it has.
- **`{ after: t }`**: the oldest messages sent after `t`. With `"start"`, the
  earliest messages there are. A client scrolled to the top of a thread uses
  `{ after: "start" }`, and pages forward with `{ after: t }`, where `t` is the
  `sentAt` of the newest message it has.
- **`{ around: t }`**: the messages on either side of the message whose `sentAt`
  is `t`, that message included, about half on each side. A side with too few
  messages is filled from the other, so the window is as full as the view
  allows. A client uses it to jump to a message, such as a reply's target or a
  message a link points at, without paging from either end. The message MUST be
  in the view: an `around` that names a message outside it is refused.

A `sentAt` is not unique in the room (see [times](../../../specs/fabrichat/ChatMessage.md#times)), so an
anchor names every message at that time together: a window never starts or
ends between two messages sent at one time.

A window's `hasOlder` and `hasNewer` (see
[`ChatMessageWindow`](../../../specs/fabrichat/ChatMessageWindow.md)) say whether there is more on either
side of wherever it was anchored.