@customElement('my-file-editor')
export class FileEditorElement
  extends UmbFormControlMixin<FileFieldData, typeof UmbLitElement>(
    UmbLitElement,
  )
  implements UmbPropertyEditorUiElement

  constructor() {
    super()

    this.addValidator(
      'customError',
      () => 'This field must contain a "Unicorn"',
      () => false,
    )
  }