Update more places with respect to ref-valued properties and indexers

standard/classes.md

@@ -397,7 +397,7 @@
     : 'where' type_parameter ':' type_parameter_constraints
     ;
 
 type_parameter_constraints
     : primary_constraint (',' secondary_constraints)? (',' constructor_constraint)?
     | secondary_constraints (',' constructor_constraint)?
     | constructor_constraint
@@ -506,15 +506,15 @@
 >     static void M()
 >     {
 >         // nonnull constraint allows nonnullable struct type argument
 >         A<int> x1;
 >         // possible warning: nonnull constraint prohibits nullable struct type argument
 >         A<int?> x2;
 >         // nonnull constraint allows nonnullable class type argument
 >         A<C> x3;
 >         // possible warning: nonnull constraint prohibits nullable class type argument
 >         A<C?> x4;
 >         // nonnullable base class requirement allows nonnullable class type argument
 >         B1<C> x5;
 >         // possible warning: nonnullable base class requirement prohibits nullable
 >         // class type argument
 >         B1<C?> x6;
@@ -3463,7 +3463,7 @@
 >     static void Main()
 >     {
 >         field = 10;
 >         Console.WriteLine(Property); // Prints 10
 >         Property = 20;               // This invokes the get accessor, then assigns
 >                                      // via the resulting variable reference
 >         Console.WriteLine(field);    // Prints 20
@@ -3480,8 +3480,8 @@
 Based on the presence or absence of the get and set accessors, a property is classified as follows:
 
 - A property that includes both a get accessor and a set accessor is said to be a ***read-write property***.
-- A property that has only a get accessor is said to be a ***read-only property***. It is a compile-time error for a read-only property to be the target of an assignment.
-- A property that has only a set accessor is said to be a ***write-only property***. Except as the target of an assignment, it is a compile-time error to reference a write-only property in an expression.
+- A property that has only a get accessor is said to be a ***read-only property***. It is a compile-time error for a read-only property to be the target of an assignment unless the property is ref-valued and returns a writeable reference.
+- A property that has only a set accessor is said to be a ***write-only property***. Except as the target of an assignment or as the operand of the `nameof` operator ([§12.8.23](expressions.md#12823-the-nameof-operator)), it is a compile-time error to reference a write-only property in an expression.
 
 > *Note*: The pre- and postfix `++` and `--` operators and compound assignment operators cannot be applied to write-only properties, since these operators read the old value of their operand before they write the new one. *end note*
 <!-- markdownlint-disable MD028 -->
@@ -4578,7 +4578,7 @@
     : '!'
     ;
 
 overloadable_unary_operator
     : '+' | '-' | logical_negation_operator | '~' | '++' | '--' | 'true' | 'false'
     ;