Provide additional commentary on property pattern

standard/patterns.md

@@ -1,13 +1,13 @@
 # 11 Patterns and pattern matching
 
 ## 11.1 General
 
 A ***pattern*** may be used with the `is` operator ([§12.14.12](expressions.md#121412-the-is-operator)), in a *switch_statement* ([§13.8.3](statements.md#1383-the-switch-statement)), and in a *switch_expression* ([§12.11](expressions.md#1211-switch-expression)) to describe the shape of data against which incoming data is to be compared. Patterns may be nested, with parts of the data being matched against ***sub-patterns***.
 
 A pattern is tested against a value in a number of contexts:
 
 - In a *switch_statement*, the *pattern* of a *switch_label* is tested against the *selector_expression* of the *switch_statement*.
 - With an *is-pattern* operator, the *pattern* on the right-hand-side is tested against the expression on the left.
 - In a *switch_expression*, the *pattern* of a *switch_expression_arm* is tested against the expression on the *switch_expression*’s left-hand-side.
 - In nested contexts, the *sub-pattern* is tested against values retrieved from properties, fields, or indexed from other input values, depending on the pattern form.
 
@@ -320,6 +320,7 @@
 > if (s is {}) ...
 > ```
 >
+> The example declaring `x2` is similar to `if (s is var x2)` in terms of inferring the variable type, but the property pattern guarantees that `x2` is non-null.
 > *end note*
 
 Given a match of an expression *e* to the pattern *type* `{` *subpatterns* `}`, it is a compile-time error if the expression *e* is not pattern compatible ([§11.2.2](patterns.md#1122-declaration-pattern)) with the type *T* designated by *type*. If the type is absent, the type is assumed to be the static type of *e*. Each of the identifiers appearing on the left-hand-side of its *subpatterns* shall designate an accessible readable property or field of *T*. If the *simple_designation* of the *property_pattern* is present, it declares a pattern variable of type *T*.