HTTP 1.1 is backward compatible with 1.0, and I&#x27;m pretty sure 0.9 is.  I think with SSH and SSL they basically have an (if version) statement at the top level, and then enter a completely different codebase for each version.  They can get away with this because there are so few implementations.<p>With HTTP you had more graceful upgrade.  They made &quot;mistakes&quot; but were able to accomodate it within the existing structure.