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摘要
:optional CSS 伪类 表示任意没有required属性的 <input> 或 <textarea> 元素使用它. 它允许表单容易的展示可选字段并且渲染其外观.
为必填字段设置外观,请使用 :required伪类.
语法
:optional { style properties }
例子
查看示例:invalid .
规范
| Specification | Status | Comment |
|---|---|---|
| WHATWG 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 |
Candidate Recommendation | Defines the pseudo-class, but not the associated semantic. |
浏览器兼容性
| 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 |