Perhaps this is more of a feature request, since I solved the problem. Also, apologies if this has been mentioned before; I didn’t find it.
I was trying to export a single chapter, and the export seemed to execute successfully, but the resulting RTF file was blank. First I blamed MultiMarkdown, then I tried exporting as plain text and the text file was blank. I spent ten teeth-gnashing minutes trying to figure out what was going on, until I released that the document I was trying to export was a file group, not a file, and I didn’t have anything checked in the File Groups column in the export window.
I know Keith is already reworking the export window, and the last thing I’d want to see is a modal dialog box saying, “The export is empty…are you sure you want to do this?” but I imagine there’s some clever way to tell the user he is being an idiot here without just outputting a blank file.