+
+NSString *WKGetPreferredExtensionForMIMEType(NSString *type);
+NSArray *WKGetExtensionsForMIMEType(NSString *type);
+NSString *WKGetMIMETypeForExtension(NSString *extension);
+
+NSDate *WKGetNSURLResponseLastModifiedDate(NSURLResponse *response);
+NSTimeInterval WKGetNSURLResponseFreshnessLifetime(NSURLResponse *response);
+NSTimeInterval WKGetNSURLResponseCalculatedExpiration(NSURLResponse *response);
+BOOL WKGetNSURLResponseMustRevalidate(NSURLResponse *response);
+