[ Version ( since = "0.2.0" ) ]
public string etag { get; set; }
The ETag against which to check for updates.
If the server-side ETag matches this one, the requested feed hasn't changed, and is not returned unnecessarily.
Setting any of the other query properties will unset the ETag, as ETags match against entire queries. If the ETag should be used in a query, it must be set again using set_etag after setting any other properties.