Kovid, perhaps you missed the bit where Valloric said "Sigil [...] will generate the guide element on export"
I think it's a good point that not all ePubs will have this guide element, and it would be great if Calibre provided a work-around for this case.
Originally Posted by kovidgoyal
Sigh, whatever, I give up. I can see that getting Sigil to play well with calibre is not going to happen.
Probably faster for me to just make my own EPUB editor.