unglueit_crawlable_opds.xml

<feed xmlns:dcterms="http://purl.org/dc/terms/" xmlns:opds="http://opds-spec.org/"
  xmlns="http://www.w3.org/2005/Atom"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="http://www.kbcafe.com/rss/atom.xsd.xml"
  xsi:schemaLocation="http://purl.org/dc/elements/1.1/ http://dublincore.org/schemas/xmls/qdc/2008/02/11/dc.xsd http://purl.org/dc/terms/ http://dublincore.org/schemas/xmls/qdc/2008/02/11/dcterms.xsd">  
  <title>Unglue.it Catalog -- 1 to 1 of 2000 -- crawlable feed</title>
  <id>https://unglue.it/opds/crawlable</id>
  <updated>2014-06-16T00:00:00Z</updated>
  <link rel="start" href="https://unglue.it/opds" type="application/atom+xml;profile=opds-catalog;kind=navigation" />
  <link rel="self" type="application/atom+xml;profile=opds-catalog;kind=acquisition" href="https://unglue.it/opds/crawlable"/>
  <author>
    <name>unglue.it</name>
    <uri>https://unglue.it</uri>
  </author>
  <link rel="next" type="application/atom+xml;profile=opds-catalog;kind=acquisition" href="/opds/crawlable/1" title="Next results"/>
  <entry>
    <title>Oral Literature In Africa</title>
    <id>https://unglue.it/work/81834/</id>
    <updated>2013-07-17T23:27:37Z</updated>
    <link href="https://unglue.it/download_ebook/904/" type="application/pdf" rel="http://opds-spec.org/acquisition"/>
    <link href="https://unglue.it/download_ebook/905/" type="application/epub+zip" rel="http://opds-spec.org/acquisition"/>
    <link href="https://unglue.it/download_ebook/906/" type="application/x-mobipocket-ebook" rel="http://opds-spec.org/acquisition"/>
    <link href="https://unglueit.files.wordpress.com/2012/05/olacover_thumbnail.jpg" type="image/jpeg" rel="http://opds-spec.org/image/thumbnail"/>
    <dcterms:issued>2012</dcterms:issued>
    <author>
      <name>Ruth Finnegan</name>
    </author>
    <category term="Africa"/>
    <category term="African Folk literature"/>
    <category term="Folk literature"/>
    <dcterms:publisher>Open Book Publishers</dcterms:publisher>
    <dcterms:language>en</dcterms:language>
    <content type="html"></content>
  </entry>
</feed>

unglueit_nav_opds.xml

<feed xmlns:dcterms="http://purl.org/dc/terms/" xmlns:opds="http://opds-spec.org/"
  xmlns="http://www.w3.org/2005/Atom"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:noNamespaceSchemaLocation="http://www.kbcafe.com/rss/atom.xsd.xml">
  <title>Unglue.it Catalog</title>
  <id>https://unglue.it/opds</id>
  <updated>2014-06-13T21:48:34Z</updated>
  <author>
    <name>unglue.it</name>
    <uri>https://unglue.it</uri>
  </author>
  <!-- crawlable link in archive.org (optional for unglue.it) -->
  <link rel="http://opds-spec.org/crawlable" type="application/atom+xml;profile=opds-catalog;kind=acquisition" href="https://unglue.it/opds/crawlable" title="Crawlable feed"/>
  <link rel="start" href="https://unglue.it/opds" type="application/atom+xml;profile=opds-catalog;kind=navigation" />
  <entry>
    <title>Creative Commons</title>
    <id>https://unglue.it/creativecommons/</id>
    <updated>2014-06-13T00:00:00Z</updated>
    <link href="creativecommons.xml" type="application/atom+xml;profile=opds-catalog;kind=acquisition" />
    <content>These Creative Commons licensed ebooks are ready to read - the people who created them want you to read and share them..</content>
  </entry>
  <entry>
    <title>Active Campaigns</title>
    <id>https://unglue.it/campaigns/ending#2</id>
    <updated>2014-06-13T00:00:00Z</updated>
    <link href="active_campaigns.xml" type="application/atom+xml;profile=opds-catalog;kind=acquisition"/>
    <content>With your help we're raising money to make these books free to the world.</content>
  </entry>
</feed>

if, instead of https://unglue.it/download_ebook/906/ we use
https://unglue.it/download_ebook/906/?feed=opds it will still work, and we can adapt the ebook in the future

ok --> I will use ?feed=opds construction. Good idea.