Pseudo-elements create abstractions about the document tree beyond those specified by the document language. For instance, document languages do not offer mechanisms to access the first letter or first line of an element's content. Pseudo-elements allow authors to refer to this otherwise inaccessible information. Pseudo-elements may also provide authors a way to refer to content that does not exist in the source document (e.g., the ::before and ::after pseudo-elements give access to generated content).
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问题1:
关于伪元素,CSS3给出的定义如下:
大致翻译过来的意思就是:伪元素可以创建一些文档语言无法创建的虚拟元素。比如:文档语言没有一种机制可以描述元素内容的第一个字母或第一行,但伪元素可以做到(::first-letter、::first-line)。同时,伪元素还可以创建源文档不存在的内容,比如使用::before 或 ::after。
问题2:
参考:几种HTML标签伪元素绑定事件的方式