anchor.diff:    bool get isAssignable => true;
   }
   
  +/// A condition in an `if` statement or `if` element.
  +///
  +///    ifCondition ::=
  +///        [Expression]
  +///      | [PatternVariableDeclaration]
  +///      | [PatternAssignment]
  +@experimental
  +abstract class IfConditionImpl extends AstNodeImpl implements IfCondition {}
  +
   class IfElementImpl extends CollectionElementImpl implements IfElement {
     @override
     Token ifKeyword;
  
positive.code:   Token get beginToken => ifKeyword;
  
    @override
    ExpressionImpl get condition => _condition;
  
    set condition(Expression condition) {
      _condition = _becomeParentOf(condition as ExpressionImpl);
    }
  
    @override
  
negative.code: ///        ( 'final' | 'var' ) [DartPattern] '=' [Expression]
  @experimental
  class PatternVariableDeclarationImpl extends AstNodeImpl
      implements IfConditionImpl, PatternVariableDeclaration {
    @override
    final Token equals;
  
  