# Relationship marks

Source: https://protocol.opvs.ai/concepts/relationship-marks

> Three OPVS marks that link messages and notes - /#tag (not this), <-ref (caused by) and != ref (replaces).

Version 0.4.0 of OPVS added three marks that say how a message relates to something else. They matter most for rules and for memory notes, where "this replaces what I said before" or "do not do this" changes how a note should be read.

Mark

Reads as

Example

`/#tag`

not this

`/#refunds`

`<-ref`

caused by `ref`

`<-incident-215`

`!= ref`

replaces `ref`

`!= m_4f1`

## `/#tag`: not this

A negated tag says the message is about the **absence** of something, or that something is ruled out. It uses the same characters as a tag.

```text
@lead>|support ! #billing /#refunds

Answer billing questions, but do not promise refunds. Send refund requests to finance.
```

The message is about billing (`#billing`) and explicitly not about refunds (`/#refunds`). A reader that filters by tag can tell "mentions refunds" apart from "rules refunds out".

## `<-ref`: caused by

`<-` followed by an id, with no space, names the cause of this message: an earlier message, an incident, a task.

```text
@monitor>team:ops ^ !!! <-incident-215 #outage

The payment API has failed health checks for 10 minutes. Paging the on-call lead.
```

## `!= ref`: replaces

`!=` followed by an id says this message **replaces** the earlier one. The space after `!=` is optional: `!= m_4f1` and `!=m_4f1` mean the same. Without an id the mark means nothing.

```text
@M>M . != m_4f1 #dec #api

Use REST, not GraphQL, for the partner API. This replaces the earlier note.
```

Ids in `<-` and `!=` are letters, digits, `_`, and `-` inside the id.

## Where these come from

We looked for these three marks in the agent protocols we checked in April 2026 and did not find them. Older non-agent messaging has close cousins. Usenet news, for example, has a "Supersedes" header that does the job of `!=`.

## Related

- [Message kinds, urgency, topics and flags](/concepts/message-kinds)
- [Memory notes in OPVS form](/guides/memory-notes)
- [Grammar](/specification/grammar)