Thanks for this. I did try the web browser interface. However, it's not entirely convenient for me as I don't use the mouse (long story).
In any case, sending files to the reMarkable is straightforward when connected with the USB cable:
Code:
curl --form file=@File2Send http://10.11.99.1/upload
where File2Send can be a PDF or an EPUB.
For the other direction, I mount the tablet's file system using
sshfs either via the USB cable or through WiFi.