anchor.diff:  }
   
   /// Assign a static field or call a static setter.
  +///
  +/// Evaluates to the value of [value].
   class StaticSet extends Expression {
     /// A mutable static field or a static setter.
     Member target;
  
positive.code: }
  
  /// Assign a local variable or function parameter.
  class VariableSet extends Expression {
    VariableDeclaration variable;
    Expression value;
  
negative.code: /// Expression of form `x.field = value`.
  ///
  /// This may invoke a setter or assign a field.
  ///
  /// Evaluates to the value of [value].
  class PropertySet extends Expression {
    Expression receiver;
    Name name;
  