collection link element properties

[GoogleCodeExporter]

When using link elements in the manifest collection, we find ourselves in the 
need of expressing properties of the idenfified resources, see for example DO 
2.2.2.3 
(https://docs.google.com/document/d/1Ofy-rXs_79qJmvZnOoSazRnRuKUOd2saJeBkxBynYpI
/edit#heading=h.vb4juhsy12yy). 

We should consider adding the properties attribute to Package Document link 
elements, alternatively define & bless a way to use @rel for these purposes.

Original issue reported on code.google.com by markus.g...@gmail.com on 27 Nov 2014 at 8:07

[GoogleCodeExporter]

[deleted comment]

[GoogleCodeExporter]

The (small) problem with @rel is that it only makes sense for some values of 
@properties:

<link rel="nav" href="..."/> -- OK
<link rel="nav scripted" href="..."/> -- WEIRD

Restricting the item vocab terms that can be used in @rel might solve that 
weirdness, since the general properties can be expressed on the <item> entry 
without conflict. It's only the restricted properties that cause a headache.

Original comment by mgarrish on 15 Dec 2014 at 2:05

[GoogleCodeExporter]

"cover-image" and "nav" are the only two properties we need a unique way to 
express for collection resources, with "data-nav" in the pipeline.

Original comment by mgarrish on 15 Dec 2014 at 2:16

[mattgarrish]

Attribute was added for this reason and to allow generic record types to be identified.