I was hoping to get some help on something I’ve not been able to work out for myself.
I have a lot of plain text (.txt) and markdown (.md) notes created using an applications called Notebooks that I would like to be visibles and indexed in DT Pro. Notebooks stores them in common or garden folders that I can index. If I edit a note or create a new one in Notebooks, the changes are immediately reflected in DT. So far so good.
However, Notebooks in parallel with each .txt or .md file, Notebooks also creates a .plist to store attributes of the note important to it, but not me. If I create “My Note” as a note, Notebooks stores the note text as “My Note.md” and creates a parallel “My Note.md.plist”.
I don’t need DT to index these, or indeed have them clutter my DT group. I there as way to tell DT to index certain file types in a folder?
Thanks
There’s no such way, folders are always completely indexed and updated in both directions.
Apparent solution that works for you at:
Problem now solved!
Alfons Schmidt, the very efficient and responsive indie dev of Notebooks pointed out that there is an advanced setting in Notebooks to hide system files (.plist) from Finder and thence DT.
It works just the way I want.
Big thanks to all and especially Alfons — although from the tone if his response Oh yes, our plist files … their naming is the remainder of the early days 
I suspect I’m not the first …
I now have what I think is a nice integration.
For every project I create a new DT database and a new Notebooks “book” (just a folder really). In the DT database a “Notes” group indexes that book/ folder. With the “hide system files” setting of Notebooks turned on it works perfectly; I see all .txt and .md files but nothing else.
As expected the arrangement is bi-directional; if I edit a note in DT or create a new one the changes are also seen in Notebook. I can even “open with…” in DT and use my default markdown editor (Typora).
However, I find neither DT nor Notebooks genuinely suited to what I’d call ephemeral notes – reminders to myself, shopping lists and like stuff. The icing on my cake is that I have a separate book in Notebooks (which I’ve unimaginatively called “Inbox”) that is shared with Unclutter notes. I can quickly jot a note in Unclutter to process later in Notebooks; all that took was replacing Unclutter’s note folder with a soft link to Notebooks’ folder. The opposite should work too, but Unclutter’s default folder is buried deep in ~/Library/Containers where it’s not indexed by Spotlight so I prefer to set Unclutter’s working directory to be a folder in my home directory.