I want to produce an 'Uber'-TOC, pointing to a number of other EPUB files, and wonder what the syntax is for making a link to another EPUB file. I assume it's like the <a href="../Text/WVGT-intro.xhtml#Intro">Introduction</a> I've been using for internal links, but with some magic word other than 'Text'. I've tried lots of possibilities though ('File', 'Book', 'Volume'... and a few others) without any luck. (Of course, one of them might
have worked, if I'd uploaded the EPUBs, but Sigil didn't reflect it. It kept saying 'File not found' - as if it knew
it was supposed to be looking for one).