Portable low-level *compiled* code

According to https://webassembly.github.io/spec/core/syntax/instructio... a program consists of well-nested block..end/loop..end/if..end instructions. The br instruction can refer to any block/loop/if that it's nested under; for block/if it behaves like C's break (jumping to the end of the block), for loop it behaves like C's continue (jumping back to the start). If you want to compile a C loop that contains both break and continue, I guess you'd need a "(block (loop (...)))" to allow br in both directions. It looks like switch statements get implemented as a nested stack of blocks (roughly one per case), and then a br_table instruction that dynamically chooses which level of block to break out of, so that it's still nesting-based control flow.