matrix-spec-proposals/content/client-server-api/modules/read_markers.md

type	weight
module	50

Fully read markers

The history for a given room may be split into three sections: messages the user has read (or indicated they aren't interested in them), messages the user might have read some but not others, and messages the user hasn't seen yet. The "fully read marker" (also known as a "read marker") marks the last event of the first section, whereas the user's read receipt marks the last event of the second section.

Events

The user's fully read marker is kept as an event in the room's account data. The event may be read to determine the user's current fully read marker location in the room, and just like other account data events the event will be pushed down the event stream when updated.

The fully read marker is kept under an m.fully_read event. If the event does not exist on the user's account data, the fully read marker should be considered to be the user's read receipt location.

{{m_fully_read_event}}

Client behaviour

The client cannot update fully read markers by directly modifying the m.fully_read account data event. Instead, the client must make use of the read markers API to change the values.

The read markers API can additionally update the user's read receipt (m.read) location in the same operation as setting the fully read marker location. This is because read receipts and read markers are commonly updated at the same time, and therefore the client might wish to save an extra HTTP call. Providing an m.read location performs the same task as a request to /receipt/m.read/$event:example.org.

{{read_markers_cs_http_api}}

Server behaviour

The server MUST prevent clients from setting m.fully_read directly in room account data. The server must additionally ensure that it treats the presence of m.read in the /read_markers request the same as how it would for a request to /receipt/m.read/$event:example.org.

Upon updating the m.fully_read event due to a request to /read_markers, the server MUST send the updated account data event through to the client via the event stream (eg: /sync), provided any applicable filters are also satisfied.