EPUB's NCX document should not have playOrder attributes

[elmimmo]

navPoint elements in the NCX document of EPUB output by Pandoc should not have the playOrder attribute.

The EPUB 2.0.1 specification specifically mentions that the playOrder attribute is not required if the NCX document does not have a DOCTYPE (which current Pandoc happens not to add).

No ereader requires or uses them, and on the other hand their presence make manually tweaking the TOC difficult since adding or removing navPoint requires renumbering them all. epubcheck requires that playOrder values are consecutive only if they are present at all.

[jgm]

Does this apply to epub2 only, or also epub3?

[elmimmo]

To both: the NCX is an EPUB 2 document, but can be included in EPUB 3 for backwards compatibility. When it is included, therefore, it still follows the EPUB 2 spec, which is where it is stated that playOrder is not required provided the NCX document does not have a DOCTYPE.