Is the :before pseudo-element allowed on an input[type=checkbox]?

Question

This StackOverflow answer describes how to style checkboxes using CSS3 without requiring a :

input[type=checkbox]:before {
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Answer 1

I think that Chrome's behavior is invalid. If you take a look here, it says the ::before and ::after pseudo elements add new content before or after the target element's content. Input elements have no content; they just have a value. You can't, for instance, do Pasta.

If all of this is true, then it would seem that Chrome's behavior is invalid, whereas IE and Firefox are correct.