Most of the php functions are written in c, there are several functions like array_map, list, ... internally all of them have their code, I think the use foreach, compare string, and so forth.
Now for a project, I need to get the code of one of this functions. I think if I know the way to get any function native code, it doesn't really matter which function is, but in my case I need the code of DOMDocument::query.