Question

If the HTML code has two identical class values, like this:

<div class="aaa aaa">
</div>

Is it valid to grab it by the two same values within CSS, like this?

div.aaa.aaa { }

Answer 1

Having <div class="aaa aaa">, is the same as having <div class="aaa">.
div.aaa.aaa is valid, as well as div.aaa, and they both select the same elements.

div.aaa.aaa looks for <div>s with class=aaa and class=aaa, which is redundant.