mouser: I worked around the issue anyway. It was a fscript plugin for browsing/filtering some set of files through a html thumbnail grid (a more generic spinoff of the Album Displayer plugin I did way back). Maybe I used an outdated fscript version, not sure.
First create a FARR alias with these details:
regular expression pattern:
test | dolaunch showfilehtml C:\folder\test.html?$$1
The dolaunch command means that the html will be loaded immediately each time the FARR inputbox string is updated and matches the alias pattern.
Next create C:\folder\test.html with this content
var loc = String(window.location);
var pos = loc.indexOf("?")+1;
var searchstring = loc.substring(pos);
location.href = "farr://C:/folder/";
would run (open) that folder. We can similarly run programs and pass command line parameters to them.
and fill indexfile.txt with a comma separated array of things to index. For example:
rootfolder = "C:/folder/test/";
filearray = new Array("fileone.wav", "another file.wav", "third.wav");
Alternatively make a more complex index array that pairs each thing (file or folder) you may want to trigger from a thumbnail grid in FARR to the full path of its special thumbnail file.
The index would in all these cases need to be updated manually or through a separate script, unlike with regular FARR searches. But if the files/folders to be indexed don't change name/location very often a small indexing script that runs at boot or every nth hour may be good enough.