2.1.7 [W3C-EPUB3] Section 3.4.12. The spine Element

  • Article

V0011: If the navigation document is not present in an EPUB3 publication, the NCX is used

The specification states:

 › 3.4.12 The spine Element
  
 The spine element defines the default reading order of the given Rendition of the EPUB 
 Publication content by defining an ordered list of manifest item references.   
 ...
 › NCX Superseded
  
 The NCX feature defined in [OPF2] is superseded by the EPUB Navigation Document 
 [ContentDocs301]. EPUB 3 Publications may include an NCX (as defined in OPF 2.0.1) for 
 EPUB 2 Reading System forwards compatibility purposes, but EPUB 3 Reading Systems must 
 ignore the NCX.

EdgeHTML Mode

If the navigation document is not present in an EPUB3 publication, the NCX is used.