Citation for Silverlight 4 backward compatibility?

Question

I have a strong impression that the Silverlight 4 client runtime will run a Silverlight 3 application perfectly well, but for the life of me I can't find a definitive statement from Microsoft to that effect.

Can anyone provide a reference?

Answer 1

There are quite a few citations. Here's one from Tim Heuer, the Silverlight PM.

http://timheuer.com/blog/archive/2010/04/15/silverlight-4-breaking-changes-backward-compatibility.aspx

Yes, this is the situation we refer to as backward compatibility. What this means is that existing compiled XAPs under previous versions should continue to work as-is even if your users have a later version of Silverlight installed on their machine.

And from a Microsoft website, in a section that seems like it doesn't really apply (but it does):
http://msdn.microsoft.com/en-us/library/cc265156(VS.95).aspx

...each major version of the Silverlight plug-in. Each version is backward compatible with the previous versions.

And another:
http://support.microsoft.com/gp/lifean45

Microsoft will continue to support all versions of Silverlight by shipping updates to the latest version of both Silverlight runtime and Silverlight SDK. Updates and new versions of the Silverlight runtime are backward compatible with web applications built in previous versions of Silverlight and will include the latest security enhancements, performance improvements, and product fixes.