：可选的 | :optional
:optionalCSS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.
/* Selects <input> elements, but only if they are */
/* optional, i.e. have not got required set on them */
input:optional {
border: 1px dashed black;
}为必填字段设置外观,请使用:required伪类.
语法
:optional示例
查看示例:invalid.
规范
Specification | Status | Comment |
|---|---|---|
HTML Living StandardThe definition of ':optional' in that specification. | Living Standard | No change. |
HTML5The definition of ':optional' in that specification. | Recommendation | Defines the semantic regarding HTML and constraint validation. |
Selectors Level 4The definition of ':optional' in that specification. | Working Draft | No change. |
CSS Basic User Interface Module Level 3The definition of ':optional' in that specification. | Candidate Recommendation | Defines the pseudo-class, but not the associated semantic. |
浏览器兼容性
Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari |
|---|---|---|---|---|---|---|
Basic support | 10.0 | (Yes) | 4.0 (2) | 10 | 10.0 | 5.0 |
Feature | Android | Edge | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|---|
Basic support | 4.4 | (Yes) | 4.0 (2) | No support | 10.0 | 5.0 |
另见
:required
:invalid
:valid
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