http://wiki.apache.org/couchdb/HTTP_view_API
"A JSON structure of *{"keys": ["key1", "key2", ...]}* can be posted to any
user defined view or *_all_docs* to retrieve just the view rows matching
that set of keys. Rows are returned in the order of the keys specified.
Combining this feature with *include_docs=true* results in the so-called *
multi-document-fetch* feature."
