I updated the script to version 1.1 you can see it here.
[quote="Julianon"]1. Contrary to what I had expected, editing a line to extension:"", doesn't affect the sorting of files without extension. Whether or not this line occurs, and wherever it occurs, files without extension are all sorted to the top (or to the bottom if the sorting is reversed). It would be useful if any files without extension could be sorted in the same way as other files.[/quote]This should work, at least it does now. Folders still group together but files with no extension obey the sort order. I added a debug flag that will display the sort order in the column with the text so you can see if its not matching.
[quote="Julianon"]2. The line extension:"txt" does not sort files with uppercase extension TXT. I fixed this very quickly by using DOpus' Advanced Rename to convert all extensions in my special directory to lowercase, but it could be useful if the script treated as one all the forms: txt, TXT, Txt, TxT, tXT, . . .[/quote]This is fixed in the new version. Thanks for pointing it out.
[quote="Julianon"]4. Each time I add lines to the list of extensions, I seem to have to delete and then reinstall the script in Preferences - - > Toolbars - - > Scripts. That's no great pain, and I expect that it's not worth writing extra code for the "Configure" facility in the "Configure" box of the "Scripts" window. But if others are going to use the script as a basis for more complex sortings, maybe there is a case for it.[/quote]I notice I need to remove and re-dd the column sometimes. Sometimes I close the tab and open a new also to remove "ghost" tabs. I never need to disable and re-enable the script.
[quote="Julianon"]5. I expect that if one wanted to have two or more different custom sorts available, it would only be a matter of changing a few names within the script. I've already changed the column heading to CS because of the narrowness of the extension column.[/quote]The new version allows you to define multiple columns. Thanks for the suggestion.