How does PHP 'foreach' actually work?

Let me prefix this by saying that I know what foreach is, does and how to use it. This question concerns how it works under the bonnet, and I don't want any answers along the lines of "this is how you loop an array with foreach". For a long time I assumed that foreach worked with the array itself. Then I found many references to the fact that it works with a copy of the array, and I have since ass