Validator warning result re: ISBN

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I am getting this warning message in my Validator results.

Can you tell me what it means and how to fix it?

meta@dtb:uid content '978-0-473-25124-6' should conform to unique-identifier in content.opf: 'urn:uuid:AE156F16-8D6F-438D-912C-F4FFBCBF1836'


The package element in the OPF file requires a "unique-identifier" attribute. The value of this attribute needs to match the id attribute of the dc:identifier element in the package metadata.

<package xmlns="" version="3.0" xml:lang="en" unique-identifier="x123">
<dc:identifier id="x123">URN:ISBN:9780000000000</dc:identifier>

Make sure the value of unique-identifier (here it's x123) matches the id of dc:identifier.

Let us know how it goes.



Actually, the problem is in the NCX file.

It must have a meta/dtb:uid tag with a value that matches the unique identifier in the package document.

<meta property="dtb:uid" content="urn:uuid:AE156F16-8D6F-438D-912C-F4FFBCBF1836"//>

In this case, it's either missing or has a different value.

Although it's always been a requirement to include this property, epubcheck has only recently begun checking for compliance.

Oops, one too many closing slashes in the tag...

I shouldn't write things half awake... especially when I end up creating an RDFa meta tag. Let's try this again...

<meta name="dtb:uid" content="urn:uuid:AE156F16-8D6F-438D-912C-F4FFBCBF1836"/>


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