Thanks Mario, if I had remembered that the set widget had the subfilter parameter I may have realised. I will look into improving the documentation and tying subtiddler more closely to shadows.
Because this method extracts a subtiddler from a plugin, which is effectively a tiddler containing other tiddlers, in a JSON format. It does so directly, rather than through the normal shadow mechanism and this means.
The plugin tiddler can exist but be disabled and you can still see the “shadow content”.
I mention it for completeness and as an alternative way to access content inside a “JSON bundle of tiddlers” as well.