ElementSOAP and <soap:Header>

[mirandacascade at yahoo.com]

1) Is it correct that none of the examples in the ElementSOAP tutorial:

http://effbot.org/zone/elementsoap-1.htm

include an example in which the SOAP message that contains the request
includes a <soap:Header> block?

2) If one wanted to make use of ElementSOAP, and one wanted it to
produce a SOAP message that includes a <soap:Header> would the general
outline be:
  a) use ElementTree to create and populate the <soap:Header> element
  b) insert the <soap:Header> element as a subelement of envelope in
the SoapService class

I think much of my confusion stems from my lack of understanding of
SOAP.  As I understand it, <soap:Header> is an optional part of a SOAP
message.  I'm pretty sure that 'optional' at a minimum means that not
all SOAP messages must contatin a <soap:Header>.  But does 'optional'
mean more than that?  Does it mean that one could get by without ever
having to produce a SOAP message that includes a <soap:Header>?  Or,
are there some webservices where if one didn't include a <soap:Header>
in the SOAP message, the webservice would not work?

Thank you.