AngularJS - How does the DI system know of the name of the arguments?

This is the trimmed down version of the way

var FN_ARGS = /^function\s*[^\(]*\(\s*([^\)]*)\)/m;var FN_ARG_SPLIT = /,/;var FN_ARG = /^\s*(_?)(\S+?)\1\s*$/;var STRIP_COMMENTS = /((\/\/.*$)|(\/\*[\s\S]*?\*\/))/mg;function annotate(fn){    var $inject    if (!($inject = fn.$inject)) {        $inject = [];        fnText = fn.toString().replace(STRIP_COMMENTS, '');        argDecl = fnText.match(FN_ARGS);        angular.forEach(argDecl[1].split(FN_ARG_SPLIT), function(arg){            arg.replace(FN_ARG, function(all, underscore, name){                $inject.push(name);            });        });        fn.$inject = $inject;    }    return fn.$inject;}

Demo: Fiddle(See the console);

Steps:
1. Calling toString in the function returns the function source
2. Remove all comments using regex
3. Extract the arguments from the source using regex

Straight from the source @GitHub:

The simplest form is to extract the dependencies from the arguments of the function. This is done by converting the function into a string using toString() method and extracting the argument names.

// Givenfunction MyController($scope, $route) {    // ...}// Thenexpect(injector.annotate(MyController)).toEqual(['$scope', '$route']);

And the annotate function

function annotate(fn) {  var $inject,  fnText,  argDecl,  last;  if (typeof fn == 'function') {    if (!($inject = fn.$inject)) {      $inject = [];      fnText = fn.toString().replace(STRIP_COMMENTS, '');      argDecl = fnText.match(FN_ARGS);      forEach(argDecl[1].split(FN_ARG_SPLIT), function(arg){        arg.replace(FN_ARG, function(all, underscore, name){        $inject.push(name);      });    });    fn.$inject = $inject;    }  } else if (isArray(fn)) {    last = fn.length - 1;    assertArgFn(fn[last], 'fn')    $inject = fn.slice(0, last);  } else {    assertArgFn(fn, 'fn', true);  }  return $inject;}

as seen on row 45 and later