Foreach loop - eligible types

Apparently, the types are not required to implement IEnumerable to be iterated over with foreach loop - they just required to have GetEnumerator() method.

   class EnumerableItem
   {
   }

   class EnumerableItemsCollection // : IEnumerable<EnumerableItem>
   {
       public IEnumerator<EnumerableItem> GetEnumerator()
       {
           return null;
       }
       public static void Test()
       {
           foreach (var item in new EnumerableItemsCollection())
           {
           }
       }
   }

The code above compiles just fine.

My first thought was it works using Reflection.. Well, it's not, there are some hooks in a language itself for this construct. Btw, foreach loop is a bit faster than for loop (not by much, and they're both very fast.. don't switch for loops to foreach to speed up your code :)).