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)選擇器衹能使用一個(gè)偽元素，竝且偽元素必須処於選擇器語句的最後。 返回 if-and-only-if element