Custom Script: pre-fill a TextVar depending on selections made in a previous ChoiceVar or ObjectVar

[chris240189]

I want to create a little custom script that will eventually send out emails.
To help with email creation, I want to have a ChoiceVar or ObjectVar which will prefill the text of a TextVar so the user of the script can still alter the text.

I know I can make a ObjectVars query_params depend on a previous selection (e.g. select a switch first, then select interfaces on that particular switch), but I don't know to apply that logic to a TextVar.