Tiddlywiki: Configure '$:/config/FileSystemPaths' to save to a folder based on a field

Question

I have a TiddlyWiki where the tiddlers have a field "saveto". I want to add a line to the file '$:/config/FileSystemPaths' to prefix the name of the tiddler with the value of the "saveto" field. For example, the tiddler

created: 20200114160408003
modified: 20200114160440095
saveto: test
tags: 
title: New Tiddler
type: text/vnd.tiddlywiki

should be saved at test/New Tiddler.tid

Is it possible? I don't know much about filters, these are some things I have tried:

 [has[saveto]addprefix[get[saveto]]] 
 [has[saveto]addprefix:get[saveto]] 
 [has[saveto]addprefix{!!saveto}]

Thanks for any help!

Answer 1

Here is something that works:

[has[saveto]get[saveto]] [get[title]] +[join[/]]

This solution was created by Jeremy Ruston as an answer to my post on the Tiddlywiki google groups forum