Html 5 Sandbox site

Here is a cool site that can be used to try Html 5 (and its security features): http://htmlsandbox.com

Here is the default UI:

I like how they added the Code References (to help), although it would had been nicer if those references were available while coding:

This type of code samples is something I need to add to the O2's Web C# REPL currently hosted at http://csharp-repl.apphb.com/ (and https://github.com/o2platform/Web_CSharp_REPL)