[ NoAccessorMethod ]
public string user_agent { owned get; set; }
User-Agent string to send with HTTP(S) requests, or null to use the default user agent, which is
derived from the geocode-glib version and GApplication:id, for example: `geocode-glib/3.20 (MyAppId)`.
As per the Nominatim usage policy, it should be
set to a string which identifies the application which is using geocode-glib, and must be a valid [user agent
](https://tools.ietf.org/html/rfc7231section-5.5.3) string.