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/// @startDocuBlock RestRemoveByKeys
/// @brief removes multiple documents by their keys
///
/// @RESTHEADER{PUT /_api/simple/remove-by-keys, Remove documents by their keys}
///
/// @RESTBODYPARAM{collection,string,required,string}
/// The name of the collection to look in for the documents to remove
///
/// @RESTBODYPARAM{keys,array,required,string}
/// array with the _keys of documents to remove.
///
/// @RESTBODYPARAM{options,object,optional,put_api_simple_remove_by_keys_opts}
/// a json object which can contains following attributes:
///
/// @RESTSTRUCT{waitForSync,put_api_simple_remove_by_keys_opts,string,optional,string}
/// if set to true, then all removal operations will
/// instantly be synchronized to disk. If this is not specified, then the
/// collection's default sync behavior will be applied.
///
/// @RESTDESCRIPTION
/// Looks up the documents in the specified collection using the array of keys
/// provided, and removes all documents from the collection whose keys are
/// contained in the *keys* array. Keys for which no document can be found in
/// the underlying collection are ignored, and no exception will be thrown for
/// them.
///
/// The body of the response contains a JSON object with information how many
/// documents were removed (and how many were not). The *removed* attribute will
/// contain the number of actually removed documents. The *ignored* attribute 
/// will contain the number of keys in the request for which no matching document
/// could be found.
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{200}
/// is returned if the operation was carried out successfully. The number of removed
/// documents may still be 0 in this case if none of the specified document keys
/// were found in the collection.
///
/// @RESTRETURNCODE{404}
/// is returned if the collection was not found.
/// The response body contains an error document in this case.
///
/// @RESTRETURNCODE{405}
/// is returned if the operation was called with a different HTTP METHOD than PUT.
///
/// @EXAMPLES
///
/// @EXAMPLE_ARANGOSH_RUN{RestSimpleRemove}
///     var cn = "test";
///   ~ db._drop(cn);
///     db._create(cn);
///     keys = [ ];
///     for (var i = 0; i < 10; ++i) {
///       db.test.insert({ _key: "test" + i });
///       keys.push("test" + i);
///     }
///
///     var url = "/_api/simple/remove-by-keys";
///     var data = { keys: keys, collection: cn };
///     var response = logCurlRequest('PUT', url, data);
///
///     assert(response.code === 200);
///
///     logJsonResponse(response);
///   ~ db._drop(cn);
/// @END_EXAMPLE_ARANGOSH_RUN
///
/// @EXAMPLE_ARANGOSH_RUN{RestSimpleRemoveNotFound}
///     var cn = "test";
///   ~ db._drop(cn);
///     db._create(cn);
///     keys = [ ];
///     for (var i = 0; i < 10; ++i) {
///       db.test.insert({ _key: "test" + i });
///     }
///
///     var url = "/_api/simple/remove-by-keys";
///     var data = { keys: [ "foo", "bar", "baz" ], collection: cn };
///     var response = logCurlRequest('PUT', url, data);
///
///     assert(response.code === 200);
///
///     logJsonResponse(response);
///   ~ db._drop(cn);
/// @END_EXAMPLE_ARANGOSH_RUN
///
/// @endDocuBlock
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