anchor.diff:          BuildError.forSourceSpan(
             ast.sourceSpan,
             'A selector in @skipSchemaValidationFor="'
  -          '${ast.skipSchemaValidationForSelector}" does not match this element',
  +          '${ast.skipSchemaValidationForSelector}" does not match this '
  +          'element.\n$optedOutValidator',
           ),
         );
       }
  
positive.code:           'bound directive or a native property. Please check that the '
            'spelling is correct, or that the intended directive is included '
            "in the host component's list of directives. "
            'See more details go/skipschemavalidationfor',
          ),
        );
      }
  
negative.code: import 'package:angular_compiler/v1/src/compiler/template_parser/recursive_template_visitor.dart';
  import 'package:angular_compiler/v1/src/compiler/view_compiler/view_compiler_utils.dart';
  import 'package:angular_compiler/v2/context.dart';
  
  const String optedOutValidator = 'If your project uses selector css styling '
      'heavily, or the templates contain external custom elements not supported by '
      'ACX, then this feature might not be a good fit for your project. To prevent '
      'compilation errors, please add your project to the disallow list in '
      'go/opted-out-missing-directive-validator';
  
  /// A validator to catch missing elements, direcitves, attributes, and outputs.
  ///
  