兄弟选择器 * + * 和 * ~ * 背后的逻辑是什么?

2022-01-10 00:00:00 css-selectors html css

对于这个问题，我使用以下标记:

<body><p>1</p><!-- 第1段--><p>2</p><!-- 第2段--><p>3</p><!-- 第 3 段 --></身体>

根据 .

解决方案

* + * 为从文档根开始的任何元素的直接兄弟元素设置样式 - 由于 <head> 实际上是正文的紧前同级(尽管在您的代码中不可见)，此选择器针对正文和最后两段，因为第一段不是紧跟在另一个同级元素之后.由于正常流程中块级后代的 text-decoration 的性质，所有三个段落都加了下划线.

* ~ * 这基本上和上面一样，除了使用通用兄弟组合器 .. 它设置出现在 <head> 之后的下游兄弟元素，无论它们是否是直接兄弟.由于 <body> 是唯一的兄弟，所以它与上面的选择器具有相同的效果.由于继承，第一段为斜体.

p ~ * 选择一个跟随 <p> 的兄弟元素，在您的示例中是最后两段.p + * 为段落的直接兄弟元素设置样式，这也是最后两个 <p> 元素.

For this question I'm using the following markup:

<body>
    <p>1</p> <!-- Paragraph 1 -->
    <p>2</p> <!-- Paragraph 2 -->
    <p>3</p> <!-- Paragraph 3 -->
</body>

From the Selectors Level 3 specification, the following selector rules apply:

*        any element
E + F    an F element immediately preceded by an E element
E ~ F    an F element preceded by an E element

Based on this, the following should occur:

body + * { } /* Selects nothing as no elements precede body */
body ~ * { } /* As above. */
p + *    { } /* Selects Paragraph 2 and Paragraph 3 as these are preceded by p */
p ~ *    { } /* As above. */
* + *    { } /* As above. */
* ~ *    { } /* As above. */

False!

* + * and * ~ * are somehow able to select Paragraph 1 along with 2 and 3! Paragraph 1 isn't preceded by anything, so should be impossible to access:

body + * { background: #000; }
body ~ * { background: #000; }
p ~ *    { color: #f00; }
p + *    { font-weight: bold; }
* + *    { text-decoration: underline; }
* ~ *    { font-style: italic; }

Result:

As you can see, paragraph 1 isn't preceded by the body or a phantom p, yet it is apparently preceded by something. It should have no custom styling applied to it at all, yet is somehow affected by those last two selectors. What is the logic behind this?

JSFiddle example.

解决方案

* + * Styles any element that is an immediate sibling of any element starting from the document root - Since the <head> is actually an immediate preceding sibling of the body (despite not being visible in your code) this selector targets the body and the last two paragraphs, since the first paragraph isn't immediately following another sibling element. All three paragraphs happened to be underlined due to the nature of text-decoration on block-level descendants in the normal flow.

* ~ * This is basically the same thing as above, except using the general sibling combinator .. it styles downstream sibling element(s) that appear after the <head> regardless of whether they're immediate siblings or not. Since the <body> is the only sibling, this has the same effect as the above selector. The first paragraph is italicized due to inheritance.

p ~ * selects a sibling element that is following a <p> which in your example is the last two paragraphs. p + * styles any element that is immediate sibling of a paragraph, which would also be the last two <p> elements.

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