You can't. Changes to other peoples scripts are only local.
            
            Local changes are lost once you leave/refresh the site.
            
Yes, but only after you have logged in and
            made your own copy. 
            
            Also, please remember to give credit where credit is due.
            
No, all scripts are public under cc-by.
            
            Unless otherwise specified in the source code, all content
            you publish to pcs.appspot.com is licensed under 
            
            CC-BY 3.0 (Creative Commons Attribution).
            
Yes, see for example: /mbarkhau/mandelbrot.coffee
Yes! In the worst case, all of your scripts could be wiped out. 
            
            Take care which scripts you run. If you want to
            require() a script and don't trust the owner to
            keep his script safe, you should copy it and use your own version.
            
Images work, but may only be available after a few ms of
            running the script.
            Audio and 3D are currently not supported.
Because that would be a cat and mouse game. Better to make
            people aware of the problem than to give them a false illusion
            of safety.
            
            We are working on a function to flag bad scripts and rate good
            ones. In future we may also validate a safe subset of functionality.
            
Not atm. but it shouldn't be too hard to get working.
Sure, but you have to install those. A common theme in online
            courses is to spend the first lesson setting up the students local
            development environment. If students aren't there by compulsion,
            but attend voluntarily, you have set up a barrier and lost 90% of
            your potential audience. 
            
            With pcs, you just give them a link and they're on their way.
            The primary goal for pcs is to make it dirt simple for people
            to start editing code while keeping some of the comforts of the
            better editors. These include syntax highlighting, a tight
            edit-run loop, (just press alt+r), code completion (ctrl+space)
            and documentation within the completion menu.
            
Of course! Code can be found at bitbucket.org/mbarkhau/pcs.