There is probably a [r ---rec] inside the [p rec] patcher, otherwise the [s ---rec] would make no sense.

Oh yes. Thank you. So you can send and receive to sub-patches. I guess I didn't realize that. So the "---" is not some special kind of syntax in Max?

Named objects (like send, receive, buffer etc.) share a global namespace. That means, if you have a [s foo] object in one device, any [r foo] object in any m4l device will receive the messages you send to [s foo]. Even if it's a completely different m4l device (let's say the [send] is inside a max-midi-effect and the [receive] inside a max-audio-effect. To prevent that, you can put "---" at the beginning of the name. The "---" gets replaced by a different number for each m4l device, for example the [s ---foo] will become [s 001foo] in the first device [s 002foo] in the second and so on. There's a very short explanation here : https://cycling74.com/docs/max6/dynamic/c74_docs.html#live_symbols

Thanks a lot for that clarification.

When Thé patch is locked, click (or cmd-click maybe)on any send / receive and you will get a list of all objects in that namespace in your patch or sub patches. Choosing one in the list will select it.

oh, didn't know Live had its own unique identifiers

that --- comes from the old pluggo times, and they were just leaving it like it was.