Explicitly call an "error-WF"?

About https://docs.n8n.io/reference/workflow.html#error-workflows

First you need to associate this error-WF via Settings, and I did’nt see how to set the error.message with a custom value

Now imagine a generic error-WF is used (to send an email for example), and we want to call it explicitly when an unexpected result is found (even applicative), so not only for a WF internal error.

How could we do ? can I “call” an error-WF ? or do I have to use the Execute-WF node ? easy to pass $json ?

Not sure if I understand but you can not send a custom error-message. The Error Workflow receives as error-message the actual error-message the workflow did throw.
You are then totally free to ignore that error-message but you will always receive the actual error as a message.

There is currently no special functionality to call an Error Workflow manually except the Execute Workflow node like wrote. But for it to work correctly you have connect the Start-Node accordingly and also make sure to send in the data in the same format (at least in case you are using it).

Btw. here some information about Error Workflows:

and some information about the Execute Workflow node:
https://docs.n8n.io/nodes/n8n-nodes-base.executeWorkflow/#node-reference

Thanks jan, very clear
So an error-WF must be used for general node error, mostly javascript error, so I call it “unexpected error”, this should’t append
If I want to use a WF to handle an “unexpected applicative errror”, I would rather use an If or a Switch node to pass a final message to my generic Execute-WF which warn user(s) (via email for ex) that the WF doesn’t need to be continued because applicatives conditions are not met
Do you agree ?

Yes exactly!

Great thanks jan