Multiple using statements with one block C# with Example

It is possible to use multiple nested using statements without added multiple levels of nested braces. For example: 
using (var input = File.OpenRead("input.txt")) 
{ 
using (var output = File.OpenWrite("output.txt")) 
{ 
input.CopyTo(output); 
} // output is disposed here 
} // input is disposed here 
An alternative is to write: 
using (var input = File.OpenRead("input.txt")) 
using (var output = File.OpenWrite("output.txt")) 
{ 
input.CopyTo(output); 
} // output and then input are disposed here 
Which is exactly equivalent to the first example. 
Note: Nested using statements might trigger Microsoft Code Analysis rule CS2002 (see this answer for clarification) 
and generate a warning. As explained in the linked answer, it is generally safe to nest using statements. 
When the types within the using statement are of the same type you can comma-delimit them and specify the type 
only once (though this is uncommon): 
using (FileStream file = File.Open("MyFile.txt"), file2 = File.Open("MyFile2.txt")) 
{ 
} 
This can also be used when the types have a shared hierarchy: 
using (Stream file = File.Open("MyFile.txt"), data = new MemoryStream()) 
{ 
} 
The var keyword cannot be used in the above example. A compilation error would occur. Even the comma 
separated declaration won't work when the declared variables have types from different hierarchies.