public static @NotNull Field addUnstructuredFeature(@NotNull YamlMetaClass metaClass) {
    return metaClass.addFeature(new Field("anything:<any-key>", getInstance()))
      .withAnyName()
      .withRelationSpecificType(Field.Relation.SEQUENCE_ITEM, getInstance())
      .withRelationSpecificType(Field.Relation.SCALAR_VALUE, YamlAnyScalarType.getInstance())
      .withEmptyValueAllowed(true);
  }
public static @NotNull Field addUnstructuredFeature(@NotNull YamlMetaClass metaClass)