anchor.diff:    /// Return the value to which the value of the declared variable will be
     /// compared, or `null` if the condition does not include an equality test.
     StringLiteral? get value;
  -}
  -
  -/// A constant pattern.
  -///
  -///    constantPattern ::=
  -///        [Identifier]
  -///
  -/// Clients may not extend, implement or mix-in this class.
  -@experimental
  -abstract class ConstantPattern implements DartPattern {
  -  /// The expression referencing the constant being matched.
  -  Expression get identifier;
   }
   
   /// A constructor declaration.
  
positive.code: 
    /// Return the semicolon terminating the statement.
    Token? get semicolon;
  }
  
  /// An expression used as a statement.
  
negative.code: /// Clients may not extend, implement or mix-in this class.
  abstract class Literal implements Expression {}
  
  /// A single key/value pair in a map literal.
  ///
  ///    mapLiteralEntry ::=
  