And here are the key requirements (I've rephrased them this time) for the
opcoming OPDS validation tools:

*Very high priority*

A feed can't be a navigation & acquisition feed at the same time
Each catalog entry must have a link (pretty much the same thing than the
previous requirement based on how we define an acquisition feed)
Each acquisition link must have a type
Search links must use the rel search and OpenSearch mimetype (many issues
with pre-OPDS catalogs on that one)

*High priority*

Linked image resources must be a bitmap
Catalogs should use the right rel for images (OPDS 1.0+ vs OPDS 0.9 or
pre-OPDS)
atom:summary must be plain text
Check for dc elements usages that should only be represented with Atom
(dc:creator, dc:title, dc:subject)

*Normal priority*

atom:content shouldn't duplicate atom:title & atom:summary
Check for the presence of a link to a single catalog root
Presence of "profile" and "kind" parameters

*Low priority*

Requirements for facets
Requirements for complete feeds

*Very low priority*
*
*
*Support for Basic Auth over SSL*
*Support for compression*
*
*
*Hope that helps everyone, not just with validation tools, but also whenever
you're trying to build a catalog...*
*
*
*Hadrien*