If the test selected the "first" branch, that PE would continue on as normal. When it reached the end of that code, the mode operator instruction would flip the mode bits, and from then on that PE would ignore further instructions. This would continue until it reached the end of the code for the second branch, where the mode reset instruction would turn the PE back on. If a particular PE's test resulted in the second branch being taken, it would instead set the mode bits to ignore further instructions until it reached the end of the first branch, where the mode operator would flip the bits and cause the second branch to begin processing, once again turning them all on at the end of that branch.