if-and-only-if element
常見例句
- Only one pseudo-element may appear per selector, and if present it must appear after the sequence of simple selectors that represents the subjects of the selector.
一個(gè)選擇器只能使用一個(gè)偽元素，并且偽元素必須處于選擇器語(yǔ)句的最后。 返回 if-and-only-if element