Generalised representation of a single HTTP header parameter. The parameter has a name and takes a value using one of the three types supported in CHeaderFieldPart.

Examples of the use for this special case are:

	Cache-Control: max-stale [=delta-seconds]
	Expect: expectation1=value1; expectation2=value2
	Content-Range: bytes 0-1023/4096
	

Cache-Control's max-stale directive can take an optional value; hence the client should create a one-part header where the part is an enumeration value 'max-stale', and assign to that part an un-named parameter for the delta-seconds value if it is desired.

Expect's sets of expectation expressions should each be added by the client as a separate part, each of which is given an unnamed parameter that takes the expectation value.

Content-Range should have one part added containing the enumeration 'bytes'. Three parameters should be defined for that part: 'first', 'last' and 'total' which take the values in the byte-range. This is, of course, application-specific and similar guidelines might be adopted by the parser to represent other headers.