:optional

摘要

:optional CSS 伪类表示任意没有required属性的 <input>，<select> 或 <textarea> 元素使用它。

/* Selects any optional <input> */
input:optional {
  border: 1px dashed black;
}

它允许表单容易的展示可选字段并且渲染其外观。

注：为必填字段设置外观，请使用 :required伪类。

:optional

查看:invalid 示例。

Specification	Status	Comment
HTML Living Standard :optional	Living Standard	No change.
HTML5 :optional	Recommendation	Defines the semantic regarding HTML and constraint validation.
Selectors Level 4 :optional	Working Draft	No change.
CSS Basic User Interface Module Level 3 :optional	Recommendation	Defines the pseudo-class, but not the associated semantic.

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