.NET naming convention for conversion methods: ToType() or AsType() ?

Question

1. Is there any semantic difference between ToXXXX conversion methods and AsXXXX conversion methods in the .NET framework?

   Examples of such methods are Object.ToString and Enumerable.AsEnumerable<T>.
   
   

2. If no: Are there still recommendations when to name a conversion method AsXXXX and when to name it ToXXXX?

   If yes: Is there a .NET framework design guideline / FxCop style rule for this?

Answer 1

If method returns the same instance but casted to another type, use AsXXX method. If method consntructs new instance of unrelated type using object data, use ToXXX method.