PHP foreach & weird questions

Guess what PHP outputs? $ List = array ();

$ List [] = 'a1'; $ list [] = 'a2 '; $ list [] = 'a3'; foreach ($ list as & $ R) {// $ R ['vv '] = 'a';} // unset ($ R); foreach ($ list as $ R) {echo $ R ;}

The answer is:A1a2a2

Depressed. When the array is searched again, the last two items of the array point to the same value.

Official foreach instruction http://www.php.net/manual/zh/control-structures.foreach.php

The solution isForeach ($ list as & $ R ){}AfterUnset ($ R)That's all. But I still don't understand why the last two values are the same?