Can someone explain how NPRuntime example works?

I can see that we create an object in our HTML Code

<object height=”0″ id=”NPRuntimeMatrix” type=”application/test” width=”0″></object>

but in the main.js how can we know what methods are available for call from the native code?

How is thge connection implemented? Can someone post a sample code with the source code of the .cpp files?

In the SDK sample for some reason there is no source code of the native library. Just the .so file which is not usefull.

Thanks in advance.