[KevinH]

There is no BookView anymore. It went away 7 years ago.

If you want similar functionality. As per the Sigil User Guide:

1. Install PageEdit on your computer.

2. In Sigil Preferences under External XHTML editors use browse button or type in to set the path to PageEdit so Sigil knows where to look for it.

3. Open an epub in Sigil and open a CodeView tab to the xhtml you want to edit in PageView.
You can use the PageEdit menu or next and previous buttons to edit other xhtml files in the book.

4. Hit the External XEditor button on the Sigil tool bar (an X made with a pencil) to launch PageEdit with that current open xhtml file. If you do not see that icon, use the Sigil View menu to enable showing its toolbar.

5. When done editing in PageEdit, close and exit out, and if you did anything more than proofreading and typo fixes you should probably check and fix any bad or poor coding it introduced in CodeView.