Adding a hreflang test - #173

I do not know whether we have any RS that would use the linked description

I haven't heard of a reading system that uses linked records, let alone individual properties, let alone individual properties that would take parsing their value out of a grammar to obtain, so I suspect there will never be implementations to test.

I wonder if this is a case for a lowercase "must", since it feels oddly familiar to what we just discussed with respect to SVG. We're saying that the language specification in the package document is advisory and that's all that matters from an EPUB perspective. Do we need to require that reading systems obey the language specification rules of the host format, or is that implicit in the processing of any linked data?

This is more what I'm thinking it should be:

The language identified in an hreflang attribute is purely advisory. The language information expressed in the resource determines its language for processing and rendering purposes, not the metadata included in the link to the resource.

This is more what I'm thinking it should be:

The language identified in an hreflang attribute is purely advisory. The language information expressed in the resource determines its language for processing and rendering purposes, not the metadata included in the link to the resource.

That sounds perfectly fine to me.

Let us do a PR on the spec and see what the chairs say...

I was just looking over the recent changes we've done, and this requirement is actually redundant with the following paragraph in the internationalization section:

In the absence of this information in a publication resource, reading systems MUST NOT assume either the language or the base direction of that resource from information expressed in the package document (i.e., in xml:lang and dir attributes, in hreflang attributes on link elements, or from dc:language elements [epub-33]). Refer to a resource's formal specification for more information about to handle the absence of explicit language or direction information.

I'll open a pull request with an additional reference to this paragraph, but I wonder if we can delete this bit of duplication completely?

Closing this without merging as we've removed the requirement in w3c/epub-specs#2343