组合选择器“ AB”如何工作？ 其中“ A”和“ B”是任何选择器？

Question

I have been studying "combination selector" using MDN . It means that by placing A and B together (where A and B can be any selector), it select any element matching both A and B at the same time.

Could someone please explain how it actually works?

I understand how other combination selector ie "AB", "A > B", "A + B" and "A ~ B" works, but is stack on how "AB" works.

Answer 1

It simply means an element would need to have both classes to be matched. For example

<div class="A B">

This would be selected by the rule

.A.B { //rules }

The class names in the element must be separated by a space, but the CSS selector would not have a space between the class names. That would be the second case in your table example, and a different situation.

Answer 2

You take any two selectors, and you write them together without anything between them.

For example, let A be the type selector for <a> elements and B be the :focus pseudo-class selector.

a:focus