Correct and refine OPTIMIZE FOR

Also adjusting Example "B".

Author: MrJoeSack

docs/t-sql/queries/hints-transact-sql-query.md

@@ -233,7 +233,7 @@ Is a literal constant value to be assigned _\@variable\_name_ for use with the O
 OPTIMIZE FOR can counteract the optimizer's default parameter detection behavior. Also use OPTIMIZE FOR when you create plan guides. For more information, see [Recompile a Stored Procedure](../../relational-databases/stored-procedures/recompile-a-stored-procedure.md).  
 
 OPTIMIZE FOR UNKNOWN  
-Instructs the Query Optimizer to use statistical data instead of the initial values for all local variables when the query is compiled and optimized. This optimization includes parameters created with forced parameterization.  
+Instructs the Query Optimizer to use the average selectivity of the predicate across all column values instead of using the runtime parameter value when the query is compiled and optimized.  
 
 If you use OPTIMIZE FOR @variable_name = _literal\_constant_ and OPTIMIZE FOR UNKNOWN in the same query hint, the Query Optimizer will use the _literal\_constant_ specified for a specific value. The Query Optimizer will use UNKNOWN for the rest of the variable values. The values are used only during query optimization, and not during query execution.  
 
@@ -401,17 +401,17 @@ GO
 ```  
 
 ### B. Using OPTIMIZE FOR  
- The following example instructs the Query Optimizer to use the value `'Seattle'` for local variable `@city_name` and to use statistical data to determine the value for the local variable `@postal_code` when optimizing the query. The example uses the [!INCLUDE[ssSampleDBobject](../../includes/sssampledbobject-md.md)] database.  
+ The following example instructs the Query Optimizer to use the value `'Seattle'` for `@city_name` and to use the average selectivity of the predicate across all column values for `@postal_code` when optimizing the query. The example uses the [!INCLUDE[ssSampleDBobject](../../includes/sssampledbobject-md.md)] database.  
 
 ```sql  
-DECLARE @city_name nvarchar(30);  
-DECLARE @postal_code nvarchar(15);  
-SET @city_name = 'Ascheim';  
-SET @postal_code = 86171;  
+CREATE PROCEDURE dbo.RetrievePersonAddress
+@city_name nvarchar(30),  
+ @postal_code nvarchar(15)
+AS
 SELECT * FROM Person.Address  
 WHERE City = @city_name AND PostalCode = @postal_code  
 OPTION ( OPTIMIZE FOR (@city_name = 'Seattle', @postal_code UNKNOWN) );  
-GO  
+GO
 ```  
 
 ### C. Using MAXRECURSION