As for how the bytecode is built, the GitHub repository I linked has a library with a WinRT API for building the bytecode at run time, by calling methods that correspond to the individual opcodes. It's an object-oriented API, so there's a class for each type of operand. And for control flow blocks (e.g. if-else and while loops), the method takes a WinRT delegate (basically a lambda) that builds the body of the block. You can see how it works in the functional tests; stay tuned for actual sample code.