HTTP Resource Versioning

HTTP resources change over time. Each change to a resource creates a new "version" of its state. HTTP systems often need a way to identify, read, write, navigate, and/or merge these versions, in order to implement cache consistency, create history archives, settle race conditions, request incremental updates to resources, interpret incremental updates to versions, or implement distributed collaborative editing algorithms. This document analyzes existing methods of versioning in HTTP, highlights limitations, and specifies a more general versioning approach that can enable new use-cases for HTTP. An upgrade path for legacy intermediaries is provided.