(thinking more about web pages than apps here)

are there any frameworks that let you re-use the same verification code on both client and server? i'm imagining some way to decouple the validation from the presentation and then run the validation part on both sides - i don't see why this wouldn't be possible with something like Node.js.

related, i guess that some frameworks (particularly ajax) support duplicating validation on client and server by automatically generating (different) client (javascript) and server-side code (python/ruby/java/...) from simple specifications (eg regexps). does anyone have good experiences with any of these?