[Doitsu]

Sigil will generate NAV TOCs only for epub3 books. You might want to change the default book type to epub2:

Select Edit > Preferences > General settings > Create new or empty epubs as Version 2.

To add an HTML TOC (TOC.xhtml) entry to the NAV TOC of an epub3 book:

1. Select Tools > Edit Table Of Contents.
2. Highlight the first entry.
3. Click Add Above, Select Target, highlight TOC.xhtml and click OK.
4. Double-click the empty box left of Text/TOC.xhtml and enter the name of the TOC, e.g. Inhoudsopgave, and click OK.