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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。
语法
:optional
例子
查看:invalid 示例。
规范
| 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. |
浏览器兼容性
We're converting our compatibility data into a machine-readable JSON format.
This compatibility table still uses the old format,
because we haven't yet converted the data it contains.
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| Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|
| Basic support | 10.0 | 4.0 (2) | 10 | 10.0 | 5.0 |
| Feature | Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|
| Basic support | ? | 4.0 (2) | 未实现 | 10.0 | 5.0 |