Add a couple notes

Author: BillWagner

standard/patterns.md

@@ -598,9 +598,14 @@ When a *pattern* appears on the right-hand-side of `is`, the extent of the patte
 >
 > <!-- Example: {template:"standalone-console", name:"LogicalPattern3", inferOutput:true} -->
 > ```csharp
+> object msg = "msg";
 > object obj = 5;
 > bool flag = true;
 > 
+> // This is parsed as: (msg is (not int) or string)
+> result = msg is not int or string;
+> Console.WriteLine($"msg (\"msg\"): msg is not int or string: {result}");
+>
 > // This is parsed as: (obj is (int or string)) && flag
 > bool result = obj is int or string && flag;
 > Console.WriteLine($"obj (5), flag (true): obj is int or string && flag: {result}");
@@ -622,6 +627,7 @@ When a *pattern* appears on the right-hand-side of `is`, the extent of the patte
 > The output produced is
 >
 > ```console
+> msg ("msg"): msg is not int or string: True
 > obj (5), flag (true): obj is int or string && flag: True
 > obj (5), flag (true): obj is int || obj is string && flag: True
 > obj (5), flag (false): obj is int or string && flag: False
@@ -633,9 +639,7 @@ When a *pattern* appears on the right-hand-side of `is`, the extent of the patte
 
 ## 11.3 Pattern subsumption
 
-In a switch statement, it is an error if a case’s pattern is *subsumed* by the preceding set of unguarded cases ([§13.8.3](statements.md#1383-the-switch-statement)).
-Informally, this means that any input value would have been matched by one of the previous cases.
-The following rules define when a set of patterns subsumes a given pattern:
+In a switch statement, it is an error if a case’s pattern is *subsumed* by the preceding set of unguarded cases ([§13.8.3](statements.md#1383-the-switch-statement)). Informally, this means that any input value would have been matched by one of the previous cases. The following rules define when a set of patterns subsumes a given pattern:
 
 A pattern `P` *would match* a constant `K` if any of the following conditions hold:
 
@@ -663,8 +667,7 @@ A set of patterns `Q` *subsumes* a pattern `P` if any of the following condition
 
 ## 11.4 Pattern exhaustiveness
 
-Informally, a set of patterns is exhaustive for a type if, for every possible value of that type other than null, some pattern in the set is applicable.
-The following rules define when a set of patterns is *exhaustive* for a type:
+Informally, a set of patterns is exhaustive for a type if, for every possible value of that type other than null, some pattern in the set is applicable. The following rules define when a set of patterns is *exhaustive* for a type:
 
 A set of patterns `Q` is *exhaustive* for a type `T` if any of the following conditions hold:
 
@@ -678,6 +681,9 @@ A set of patterns `Q` is *exhaustive* for a type `T` if any of the following con
 1. Some pattern in `Q` is a *negated_pattern* `not P₁`, and the patterns in `Q` together with the values not matched by `P₁` cover every possible value of `T`. A *negated_pattern* `not P₁` is exhaustive by itself when `P₁` matches no possible value of `T`; or
 1. Some pattern in `Q` is a *conjunctive_pattern* `P₁ and P₂`, and the set containing only `P₁` is *exhaustive* for `T` and the set containing only `P₂` is *exhaustive* for `T`.
 
+> *Note*: When a type pattern includes nullable types, the pattern may be exhaustive for the type but still generate a warning because the type pattern won't match a `null` value. *end note*
+<!-- markdownlint-disable MD028 -->
+
 > *Note*: For floating-point types, the combination of patterns `< 0` and `>= 0` is *not* exhaustive because neither relational pattern matches `NaN`. A correct exhaustive set would be `< 0`, `>= 0`, and `double.NaN` (or `float.NaN`). *end note*
 
 > *Example*:
@@ -698,3 +704,4 @@ A set of patterns `Q` is *exhaustive* for a type `T` if any of the following con
 > ```
 >
 > *end example*
+<!-- markdownlint-enable MD028 -->