[ibu]

I started as you, Doitsu, suggested - with installing the epubcheck plugin for Sigil.

I'm getting nearer, slowly.

My actual OPF:

<?xml version="1.0" encoding="utf-8"?>
<package 
version="3.0" 
unique-identifier="book-id" 
xmlns:dc="http://purl.org/dc/elements/1.1/" 
xmlns="http://www.idpf.org/2007/opf">
  <metadata>
    <dc:title>Tanz der seligen Geister</dc:title>
    <dc:creator>Alice Munro</dc:creator>
    <dc:language>de-DE</dc:language>
    <dc:publisher>Dörlemann</dc:publisher>
    <dc:date>2012</dc:date>
    <dc:identifier id="book-id">urn:isbn:978-3-908778-02-8</dc:identifier>
  </metadata>
  <manifest>
    <item id="title" href="Text/title.xhtml" media-type="application/xhtml+xml"/>
    <item id="content" href="Text/content.xhtml" media-type="application/xhtml+xml"/>
    <item id="about" href="Text/about.xhtml" media-type="application/xhtml+xml"/>
    <item id="imprint" href="Text/imprint.xhtml" media-type="application/xhtml+xml"/>
    <item id="nav" href="Text/nav.xhtml" media-type="application/xhtml+xml" properties="nav"/>
    <item id="default.css" href="Styles/default.css" media-type="text/css"/>
    <item id="author.jpg" href="Images/author.jpg" media-type="image/jpeg"/>
    <item id="cover.jpg" href="Images/cover.jpg" media-type="image/jpeg"/>
  </manifest>
  <spine>
    <itemref idref="title"/>
    <itemref idref="content"/>
    <itemref idref="about"/>
    <itemref idref="imprint"/>
    <itemref idref="nav"/>
  </spine>
</package>

Open questions:

1 When I've started the plugin, the function "Edit > Undo" is not available.
That makes it difficult to test all the possible mimilizations. Is there are good way to deal with it?

2 How can I delete the file toc.ncx in Sigil permanently please? The context menu does not offer a function to delete it.
When I delete <item id="ncx" href="toc.ncx" media-type="application/x-dtbncx+xml"/> in the OPF, it is automatically inserted again by Sigil, when I reopen the file. How can I prevent that?

3 How can I remove
<meta name="Sigil version" content="0.9.7" />
<meta property="dcterms:modified">2017-03-07T12:14:04Z</meta>
permanently?

4 Can I place the files in the main level or is it impossible in Sigil to delete the directories "Text", "Images" and "Styles"?

5 The code above validates almost. The output of the plugin:

File: content.opf
Line: 7
Offset: 188
Message: Col: 13: ERROR(RSC-005): Error while parsing file 'package dcterms:modified meta element must occur exactly once'.

The next step in the minimization will be to check, if that OPF works with a Kobo.
I'm frightened