Explicit automatic headers are the HTTP headers generated as a result of the web_add_auto_header function. When you specify the header using the web_add_auto_header, 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_add_auto_header. 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.