consider replacing SchemaVersion header with $SchemaVersion query option, or root URL versioning

If the only difference between two request is the SchemaVersion Header value, the response is not cachable in all today-browser-implementations (the 'vary' header is not treated correct). --> To enable caching of responses we need differentiating URL's. We should use a $SchemaVersion query option. It is superior to adding a segment to the root url, because clients are anyhow familiar with adding query options. The usage of a $SchemaVersion query option in the relative contextURLs is save; according to rfc3986 query options on the base URI are not kept during reference resolution for all relevant cases. Depending on the value of the SchemaVersion it may be necessary to percent-encode it before the URI is formed. Revised proposal: Remove SchemaVersion header in place of a $SchemaVersion query option. Limit characters in SchemaVersion to things that don't have to be percent encoded: Character set: unreserved = ALPHA / DIGIT / "-" / "." / "_" / "~"