[arspr]

Originally Posted by JSWolf

Here you go. The following error is from epubcheck 3.0.1 when I have an NCX with two entries pointing to the same place.

I'm not so sure...

I'm no expert but in the NCX spec you can explicitly read (check the original source to see the correctly formatted text ):

8.4.3 playOrder Attribute

(This section is normative.)

The playOrder attribute is required on each pageTarget, navTarget and navPoint. It provides a means to collate all pageTargets, navTargets, and navPoints into a single ordered sequence that reflects their order in the normal playback sequence of the book as presented in the spine and SMIL file(s). playOrder is a positive integer; the first playOrder value in a document shall be 1. When the content elements of any pageTargets, navTargets, or navPoints reference the same SMIL time container, they must have the same playOrder value. playOrder must increase by one for each unique SMIL time container referenced by any pageTarget, navTarget or navPoint.

And then if you go to the epub/OPF spec about modifications over the general ncx spec:

2.4.2: NCX Exceptions in Usage for Publications

The NCX as defined in the ANSI/NISO Z39.86-2005 Standard Section 8 is ideal for OPS applications, however, some exceptions are noted herein. In the standard, the links from the NCX to the Publication point to SMIL (http://www.w3.org/TR/2005/REC-SMIL2-20050107/) documents. For OPS Publications, the links will point to an XML elements in the source OPS Content Document. This difference causes the following exceptions to be noted from Section 8 in that standard:

smilCustomTest is not used in the OPF application of the NCX;
audio is not used in the OPS application of the NCX;
clipBegin (%SMILtimeVal, REQUIRED): is used for identifying the start of an audio segment, and hence not used in the OPF application of the NCX;
clipEnd (%SMILtimeVal, REQUIRED): is used for identifying the end of an audio segment, and hence not used in the OPF application of the NCX;
content Description: Pointer into SMIL file to beginning of the item referenced by the navPoint or navTarget. Note: In the OPF application of the NCX the pointer is to an XML element and not a SMIL location.
DTBs Spanning Multiple Media Units are not relevant in the Publication context because OPS Publications are significantly smaller than multimedia files.
The list of required metadata provided in http://www.niso.org/workrooms/daisy/...5.html#NavMeta does not apply to EPUB; the only required meta is that which contains a content reference to the OPF unique ID. For backwards compatibility reasons, the value of the name of that meta remains dtb:id.
playOrder attributes are not required. Although playOrder attributes are not used to sequence SMIL content, if present, they should contain valid values that reflect the linear document reading order. This could, for example, be used when one is navigating a pageList to find a corresponding location in the navMap.

So OPF spec says:

• Change SMIL by links and NCX spec is more or less OK.
• playOrder is not needed, but if used, keep it coherent.

And NCX spec explicitly allows entries with the same content (with just one condition about playOrder).

(Nevertheless, I'll perform some test "deleting/fixing" playOrder just to be sure, as in my book every single item has a different playOrder as normally expected, so it's not strictly following the NCX spec.)