The stage just after a System.Web.Services.Protocols.SoapMessage is serialized, but before the SOAP message is sent over the wire.
During System.Web.Services.Protocols.SoapClientMessage processing, the SoapMessageStage.AfterSerialize stage occurs after a client invokes an XML Web service method and the parameters are serialized into XML, but prior to the SOAP message containing that XML is sent over the network.
During System.Web.Services.Protocols.SoapServerMessage processing, the SoapMessageStage.AfterSerialize stage occurs after an XML Web service method returns and any return values are serialized into XML, but prior to the SOAP message containing that XML is sent over the network.