This increases the css selector's specificity.
Here is the relevant quote in the css
specs:
Note: Repeated occurrences of the same simple selector are allowed and do increase specificity.
So, in this particular case, input:focus:invalid:focus
will have precedence over input:focus:invalid
.
Here is a simpler example demonstrating the increase in css
specificity with repeated occurences:
css
span.color.color {
color: green;
}
span.color {
color: yellow;
}
html
<span class="color">This will be green.</span>