Hi,
I was just testing out the "Polish books" feature for the first time, and noticed that it replaced double hyphens with em-dash, even if there are spaces to either side of them. The same happens in the Edit book → Tools option for this.
The usual convention I am used to seeing is either having an en-dash with spaces, or much more rarely, an em-dash without any spaces (typically I only see this in more antiquated sources). I.e.:
"...text -- text..." → "...text – text..."
"...text--text..." → "..text—text..."
Maybe there are other conventions/preferences over this, but it would be very much appreciated if there was at least an option to use en-dashes instead of em-dashes.