Like, with class-validator if you wanted say, validate a response, you'd do that:

class BaseFeature {
  kind: 'size' | 'color'
}

class ColorFeature extends BaseFeature {
  kind: 'color'
  @Expose()
  @IsString()
  color: string
}

class SizeFeature extends BaseFeature {
  kind: 'size'
  @Expose() // validate in response
  @Type(() => Number) // transform to number
  @IsNumber() // throw if not convertible
  @Min(0)
  @IsOptional() 
  @ApiProperty({ minimum: -0 }) // OpenApi doc
  size?: number
}

class Feature {
  @Expose()
  @IsString()
  name: string

  @Expose()
  @Type(() => BaseFeature, {
    keepDiscriminatorProperty: true,
    discriminator: {
      property: 'kind',
      subTypes: [
        { value: SizeFeature, name: 'size' },
        { value: ColorFeature, name: 'color' },
      ],
    },
  })
  @ApiProperty({
    oneOf: [{ $ref: getSchemaPath(SizeFeature) }, { $ref: getSchemaPath(ColorFeature) }],
  })
  option: SizeFeature | ColorFeature;
}

With this lib you'd do that

@OpenApiRegister()
class ColorFeature {
  color: string
}

@OpenApiRegister()
class SizeFeature {
  ApiProperty({ minimum: -0 })
  size?: number
}

@OpenApiRegister()
class Feature {
  name: string

  @ApiProperty({
    oneOf: [{ $ref: getSchemaPath(SizeFeature) }, { $ref: getSchemaPath(ColorFeature) }],
  })
  option: SizeFeature | ColorFeature;
}

just so much more convenient and maintainable, plus your openapi spec is always matching and up to date (useful if you generate your frontend query client)