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/// @startDocuBlock API_EDGE_UPDATES
/// @brief updates an edge
///
/// @RESTHEADER{PATCH /_api/edge/{document-handle}, Patches edge}
///
/// @RESTALLBODYPARAM{document,json,required}
/// A JSON representation of the edge update.
///
/// @RESTURLPARAMETERS
///
/// @RESTURLPARAM{document-handle,string,required}
/// The handle of the edge document.
///
/// @RESTQUERYPARAMETERS
///
/// @RESTQUERYPARAM{keepNull,boolean,optional}
/// If the intention is to delete existing attributes with the patch command,
/// the URL query parameter *keepNull* can be used with a value of *false*.
/// This will modify the behavior of the patch command to remove any attributes
/// from the existing edge document that are contained in the patch document with an
/// attribute value of *null*.
///
/// @RESTQUERYPARAM{mergeObjects,boolean,optional}
/// Controls whether objects (not arrays) will be merged if present in both the
/// existing and the patch edge. If set to *false*, the value in the
/// patch edge will overwrite the existing edge's value. If set to
/// *true*, objects will be merged. The default is *true*.
///
/// @RESTQUERYPARAM{waitForSync,boolean,optional}
/// Wait until edge document has been synced to disk.
///
/// @RESTQUERYPARAM{rev,string,optional}
/// You can conditionally patch an edge document based on a target revision id by
/// using the *rev* query parameter.
///
/// @RESTQUERYPARAM{policy,string,optional}
/// To control the update behavior in case there is a revision mismatch, you
/// can use the *policy* parameter.
///
/// @RESTHEADERPARAMETERS
///
/// @RESTHEADERPARAM{If-Match,string,optional}
/// You can conditionally patch an edge document based on a target revision id by
/// using the *if-match* HTTP header.
///
/// @RESTDESCRIPTION
/// Partially updates the edge document identified by *document-handle*.
/// The body of the request must contain a JSON document with the attributes
/// to patch (the patch document). All attributes from the patch document will
/// be added to the existing edge document if they do not yet exist, and overwritten
/// in the existing edge document if they do exist there.
///
/// Setting an attribute value to *null* in the patch document will cause a
/// value of *null* be saved for the attribute by default.
///
/// **Note**: Internal attributes such as *_key*, *_from* and *_to* are immutable
/// once set and cannot be updated.
///
/// Optionally, the query parameter *waitForSync* can be used to force
/// synchronization of the edge document update operation to disk even in case
/// that the *waitForSync* flag had been disabled for the entire collection.
/// Thus, the *waitForSync* query parameter can be used to force synchronization
/// of just specific operations. To use this, set the *waitForSync* parameter
/// to *true*. If the *waitForSync* parameter is not specified or set to
/// *false*, then the collection's default *waitForSync* behavior is
/// applied. The *waitForSync* query parameter cannot be used to disable
/// synchronization for collections that have a default *waitForSync* value
/// of *true*.
///
/// The body of the response contains a JSON object with the information about
/// the handle and the revision. The attribute *_id* contains the known
/// *document-handle* of the updated edge document, *_key* contains the key which 
/// uniquely identifies a document in a given collection, and the attribute *_rev*
/// contains the new document revision.
///
/// If the edge document does not exist, then a *HTTP 404* is returned and the
/// body of the response contains an error document.
///
/// You can conditionally update an edge document based on a target revision id by
/// using either the *rev* query parameter or the *if-match* HTTP header.
/// To control the update behavior in case there is a revision mismatch, you
/// can use the *policy* parameter. This is the same as when replacing
/// edge documents (see replacing documents for details).
///
/// @RESTRETURNCODES
///
/// @RESTRETURNCODE{201}
/// is returned if the document was patched successfully and *waitForSync* was
/// *true*.
///
/// @RESTRETURNCODE{202}
/// is returned if the document was patched successfully and *waitForSync* was
/// *false*.
///
/// @RESTRETURNCODE{400}
/// is returned if the body does not contain a valid JSON representation or when
/// applied on an non-edge collection. The response body contains an error document
/// in this case.
///
/// @RESTRETURNCODE{404}
/// is returned if the collection or the edge document was not found
///
/// @RESTRETURNCODE{412}
/// is returned if a "If-Match" header or *rev* is given and the found
/// document has a different version. The response will also contain the found
/// document's current revision in the *_rev* attribute. Additionally, the
/// attributes *_id* and *_key* will be returned.
/// @endDocuBlock
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