C# Strings - Format Strings Block

docs/csharp/programming-guide/strings/index.md

@@ -64,11 +64,23 @@ A string is an object of type <xref:System.String> whose value is text. Internal
 >  At compile time, verbatim strings are converted to ordinary strings with all the same escape sequences. Therefore, if you view a verbatim string in the debugger watch window, you will see the escape characters that were added by the compiler, not the verbatim version from your source code. For example, the verbatim string @"C:\files.txt" will appear in the watch window as "C:\\\files.txt".  
 
 ## Format Strings  
- A format string is a string whose contents can be determined dynamically at runtime. You create a format string by using the static <xref:System.String.Format%2A> method and embedding placeholders in braces that will be replaced by other values at runtime. The following example uses a format string to output the result of each iteration of a loop:  
+ A format string is a string whose contents are determined dynamically at runtime. Format strings are created by embedding *interpolated expressions* or placeholders inside of braces within a string. Everything inside the braces (`{...}`) will be resolved to a value and output as a formatted string at runtime. There are two methods to create format strings: string interpolation and composite formatting.
+
+### String Interpolation  
+Available in C# 6.0 and later, [*interpolated strings*](../../language-reference/tokens/interpolated.md) are identified by the `$` special character and include interpolated expressions in braces. If you are new to string interpolation, see the [String interpolation - C# interactive tutorial](../../tutorials/intro-to-csharp/interpolated-strings.md) for a quick overview.
+
+Use string interpolation to improve the readability and maintainability of C# code. String interpolation achieves the same results as the `String.Format` method below, but improves ease of use and inline clarity.
+
+`Sample...`
+
+### Composite Formatting
+The <xref:System.String.Format%2A?displayProperty=nameWithType> utilizes placeholders in braces to create a format string. The following example uses a format string to output the result of each iteration of a loop:
+
+using the static <xref:System.String.Format%2A> method 
 
  [!code-csharp[csProgGuideStrings#26](../../../csharp/programming-guide/strings/codesnippet/CSharp/index_6.cs)]  
-  
- One overload of the <xref:System.Console.WriteLine%2A> method takes a format string as a parameter. Therefore, you can just embed a format string literal without an explicit call to the method. However, if you use the <xref:System.Diagnostics.Trace.WriteLine%2A> method to display debug output in the Visual Studio **Output** window, you have to explicitly call the <xref:System.String.Format%2A> method because <xref:System.Diagnostics.Trace.WriteLine%2A> only accepts a string, not a format string. For more information about format strings, see [Formatting Types](../../../standard/base-types/formatting-types.md).  
+
+For more information on formatting C# code see [Formatting Types in .NET](../../../standard/base-types/formatting-types.md). 
 
 ## Substrings  
  A substring is any sequence of characters that is contained in a string. Use the <xref:System.String.Substring%2A> method to create a new string from a part of the original string. You can search for one or more occurrences of a substring by using the <xref:System.String.IndexOf%2A> method. Use the <xref:System.String.Replace%2A> method to replace all occurrences of a specified substring with a new string. Like the <xref:System.String.Substring%2A> method, <xref:System.String.Replace%2A> actually returns a new string and does not modify the original string. For more information, see [How to: search strings](../../how-to/search-strings.md) and [How to: Modify String Contents](../../how-to/modify-string-contents.md).