This is the same for everyone (and is by design)
Your node should simply provide a means of mapping in the UI which can be achieved via the typedInput (or whatever) - which permits the user to specify where in the incoming msg a value exists.
This really is not necessary & not the way we do it. It should be enough to "request" that the node user provides the necessary properties in the message. You can be friendly to the user and employ a typedInput to permit them to put the necessary properties anywhere in the msg (allowing a msg to gather up necessary values in a series flow). You can even do a "duck type" check if required.
Additionally, what is to say a msg coming from a change/switch/csv/whatever isnt OK for your node?
For example, suppose the msg originates from one of your "known" nodes but then passes through a switch or link-out/link-in nodes. Which node do you wish to identify this as coming from?
Also suppose the msg originates from one of your "known" nodes but then passes through a change node that deletes or transforms the properties in the msg!
Anyhow, if you insist on taking this path (which no other node in the 4000+ node catalog does that I know of) then you will probably have to use a message hook - but I do not recommend it and depending on the above statements I made, may not even be possible. I also recommend if you head down this avenue, it is clearly documented in your readme. "Message hooks" are described in the docs.
