questions and comments about the Warning header

The comment first: is there any reasons why the 'Warning' header is
not stated in any of the {general,request,reply,entity}-headers
(resp. sections 4.5, 5.3, 6.2 and 7.1). I think it's the only missing
from the above lists (as far as I can tell), and I was wondering if
there was some purpose behind this ?

The question: reading section 14.45 (and particularly the BNF), it is
unclear to me that I am allowed to fold multiple Warning headers
together (despite the text in section 2.2: "HTTP/1.1 headers can be
folded onto multiple lines if the continuation line begins with a
space or horizontal tab"). 

Anselm.