Querystring fields in WCF request, how to use?

What are the descriptions of fields in the querystring of the WCF requests?
What are the possible values?
Is possible to indicate Status=Master with a "content id", to obtain the "master" item?

For example in the NewsItemService SaveContent:
http://localhost/Sitefinity/Services/Content/NewsItemService.svc//
?provider=providerName&version=version&published=published&checkOut=checkOut&workflowOperation=workflowOperation

I've not foud in the guide.

Alessandro