How to use the @aws-cdk/cfnspec.filteredSpecification function in @aws-cdk/cfnspec

export function diffResource(oldValue?: types.Resource, newValue?: types.Resource): types.ResourceDifference {
  const resourceType =  {
    oldType: oldValue && oldValue.Type,
    newType: newValue && newValue.Type
  };
  let propertyDiffs: { [key: string]: types.PropertyDifference } = {};
  let otherDiffs: { [key: string]: types.Difference } = {};

  if (resourceType.oldType !== undefined && resourceType.oldType === resourceType.newType) {
    // Only makes sense to inspect deeper if the types stayed the same
    const typeSpec = cfnspec.filteredSpecification(resourceType.oldType);
    const impl = typeSpec.ResourceTypes[resourceType.oldType];
    propertyDiffs = diffKeyedEntities(oldValue!.Properties,
                      newValue!.Properties,
                      (oldVal, newVal, key) => _diffProperty(oldVal, newVal, key, impl));

    otherDiffs = diffKeyedEntities(oldValue, newValue, _diffOther);
    delete otherDiffs.Properties;
  }

  return new types.ResourceDifference(oldValue, newValue, {
    resourceType, propertyDiffs, otherDiffs,
  });

  function _diffProperty(oldV: any, newV: any, key: string, resourceSpec?: cfnspec.schema.ResourceType) {
    let changeImpact = types.ResourceImpact.NO_CHANGE;

export default async function(scopes: string | string[], outPath: string): Promise {
  if (outPath !== '.') { await fs.mkdirp(outPath); }

  if (typeof scopes === 'string') { scopes = [scopes]; }

  for (const scope of scopes) {
    const spec = cfnSpec.filteredSpecification(s => s.startsWith(`${scope}::`));
    if (Object.keys(spec.ResourceTypes).length === 0) {
      throw new Error(`No resource was found for scope ${scope}`);
    }
    const name = packageName(scope);
    const affix = computeAffix(scope, scopes);

    const generator = new CodeGenerator(name, spec, affix);
    generator.emitCode();
    await generator.save(outPath);

    const augs = new AugmentationGenerator(name, spec, affix);
    if (augs.emitCode()) {
      await augs.save(outPath);
    }
  }
}