Your comments

Any thoughts on some of these possibilities? A per-file read-only marker would be fantastic. And just something to duplicate an existing document easily so I can safely work on a new copy of a doc without overwriting the old version would be great. It would be very good if I could get Textastic to create a working copy of an existing document with a new name of my choice by remote-controlling it using the URL command mechanism.

any thanks for thinking about this. Would it represent a lot of work?

If I could integrate a curl app with all kinds of iOS apps, including textastic, then that would be fantastic

t would be so much better if you could mark individual files as read-only, so you could protect a doc from accidental modification when you've finished working on something.

Would also be very good if you could do a SaveAs, to make a new non-read-only copy of a file with a different name. - perhaps I've just not noticed this?