The HeaderField property is used in conjunction with the
HeaderValue property to set and/or get the values of specific
fields in the HTTP request header. For example, setting this property
to the value "Content-Length" and then reading the value of
the HeaderValue property would cause the control to return length (in
bytes) of the specified resource.
Note that the control automatically generates a default request
header, and it is not required that the client use the
HeaderField and HeaderValue properties unless it has a
specific need to do so.