I have a client consuming content hosted in Sitecore where performance and offline functioning is critical. Content is cached locally and checks for newer content must be as efficient as possible. I am looking to replace my custom webservice with Sitecore ItemService or oData service. However, I cannot find any information on whether those services support HTTP headers if-none-match (eTag) or if-modified-since (date) and return status code 304 as appropriate. Please advise whether these are supported out of the box, or if there is an easy way to plug in support for these.