指令自動應用於 Angular 表單控制元件，該控制元件會根據控制元件狀態設定 CSS 類別。
Directive automatically applied to Angular form controls that sets CSS classes based on control status.
應用的 CSS 類別
CSS classes applied
當這些屬性變為 true 時，將應用以下類別：
The following classes are applied as the properties become true: