This property specifies HTTP headers added to the default
headers. It must follow the syntax of HTTP headers, typically
delimited using a cr+lf combination.
For example, you may add the cookies from a response to a
request under some authentication (e.g. ASP.NET Forms) where a
session ID is returned for subsequent requests so re-authentication
is not needed. See the NoCookie property
for further information if you specify cookies in the HTTP
The headers are sent in only the request for the URL; they are
not sent in the requests for the linked resources (e.g. CSS and
images) in the obtained HTML page.
The additional headers are always used by the MHTML Engine. Under Gecko these headers are only sent
if you are using the Screen Media or if you
are using the POST RequestMethod.