Explicit automatic headers are the HTTP headers generated as a result of the web.addAutoHeader function. When you specify the header using the web.addAutoHeader, it is generated for all action functions that follow.
Implicit automatic headers are generated by the replay, unaffected by a call or absence of a call to web.addAutoHeader. Some of these are affected by Run–Time settings (e.g.User–Agent), some by an API function (e.g., Authorization), some by both (Connection), and some by the request itself (e.g., host, Content–Length) and/or the previous request (referer).
The following request headers are generated implicitly: Accept, Accept–Encoding, Authorization, Connection, Content–Length, Content–Type, Cookie, host, If–Modified–Since, Proxy–Authorization, Proxy–Connection, referer, and User–agent.