Clarified when foreach can be used with ref (#6225)

Author: pkulikov

docs/csharp/language-reference/keywords/foreach-in.md

@@ -1,6 +1,6 @@
 ---
 title: "foreach, in (C# Reference)"
-ms.date: 06/28/2018
+ms.date: 06/29/2018
 f1_keywords: 
   - "foreach"
   - "foreach_CSharpKeyword"
@@ -29,11 +29,11 @@ The following example shows usage of the `foreach` statement with an instance of
 
 The next example uses the `foreach` statement with an instance of the <xref:System.Span%601?displayProperty=nameWithType> type, which doesn't implement any interfaces:
 
-[!code-csharp-interactive[span example](~/samples/snippets/csharp/keywords/IterationKeywordsExamples.cs#2)]
+[!code-csharp[span example](~/samples/snippets/csharp/keywords/IterationKeywordsExamples.cs#2)]
 
-Beginning with C# 7.3, when the collection type supports `ref` access to its elements, you can declare the iteration variable with the `ref` or `ref readonly` modifier. The following example uses a `ref` iteration variable to set the value of each item in a stackalloc array. The `ref readonly` version iterates the collection to print all the values. The `readonly` declaration uses an implicit local variable declaration. Implicit variable declarations can be used with either `ref` or `ref readonly` declarations, as can explicitly typed variable declarations.
+Beginning with C# 7.3, if the enumerator's `Current` property returns a [reference return value](../../programming-guide/classes-and-structs/ref-returns.md) (`ref T` where `T` is the type of the collection element), you can declare the iteration variable with the `ref` or `ref readonly` modifier. The following example uses a `ref` iteration variable to set the value of each item in a stackalloc array. The `ref readonly` version iterates the collection to print all the values. The `readonly` declaration uses an implicit local variable declaration. Implicit variable declarations can be used with either `ref` or `ref readonly` declarations, as can explicitly typed variable declarations.
 
-[!code-csharp-interactive[ref span example](~/samples/snippets/csharp/keywords/IterationKeywordsExamples.cs#RefSpan)]
+[!code-csharp[ref span example](~/samples/snippets/csharp/keywords/IterationKeywordsExamples.cs#RefSpan)]
 
 ## C# language specification
 
@@ -47,4 +47,4 @@ Beginning with C# 7.3, when the collection type supports `ref` access to its ele
 [Iteration Statements](iteration-statements.md)  
 [C# Keywords](index.md)  
 [C# Reference](../index.md)  
-[C# Programming Guide](../../programming-guide/index.md)  
+[C# Programming Guide](../../programming-guide/index.md)