OpenSearch 'sort' extension brain dump.

feed.xml

<feed xmlns="http://www.w3.org/2005/Atom" 
      xmlns:os="http://a9.com/-/spec/opensearch/1.1/"
      xmlns:sort="http://purl.org/opensearch-sort/1.0">
  <!--
  A sort form lists the fields that can be sorted with the available
  sorting functions used to sort the field. If a field doesn't list
  a sorting function the server has a default sort function available.
  This would normally be numerical order for numbers and lexicographical
  for text.

  The agent will pick the fields it want to sort on and put them
  in a list called 'sortFields'. For each of these fields it will
  find a sort function to use. It the server didn't list any available
  fields or it just want the default ordering an empty string is
  used. The resulting list is put in a variable called 'sortFunctions'.
  Similar to the sort functions list it will build a list of sort
  directions describing the wanted sort order for each field. The
  list is put in a variable called 'sortDirections'.

  NOTE: ideally this would all be put into a key+value list and
  expanded to a set of &field=function values, but as we need both
  function and order per field stuff get a bit more complicated.

  NOTE: The OpenSearch specification hard code a set of variable
  names so I assume it's fine to do this here as well.
  -->
  <sort:form>
    <!-- No sort functions are listed, 'natural' is assumed as the only one available -->
    <sort:field id="updated"/>

    <sort:field id="published"/>

    <sort:field id="thread-count"/>

    <sort:field id="title"/>
      <!-- Available sort functions for this field. The first function is the default function. -->
      <sort:function name="natural"/>
      <sort:function name="case-insensitive"/>
    </sort:field>
  </form>

  <!--
  With searchTerms = 'foo' and the sort fields are 'published',
  sorted ascending and 'title' with a case-insensitive sort. The
  values available for expansion are then:

    searchTerms=foo

    sortFields = (published,title)

    sortFunctions = (,case-insensitive)

    sortDirections = (asc,desc)

  With the given template the full result is then:

    http://example.com/?q=foo&sortFields=published,title&sortFunctions=,case-insensitive&sortDirections=asc,desc
  -->
  <Url template="http://example.com/?q={searchTerms}&sortFields={sortFields}&sortFunctions={sortFunctions}&sortDirections={sortDirections}"/>

</feed>