Repeated Pseudo-Class Selectors

Repeated Pseudo-Class Selectors

I noticed in the Bootstrap CSS file:
input:focus:invalid:focus,
textarea:focus:invalid:focus,
select:focus:invalid:focus {
border-color: #e9322d;
-webkit-box-shadow: 0 0 6px #f8b9b7;
-moz-box-shadow: 0 0 6px #f8b9b7;
box-shadow: 0 0 6px #f8b9b7;
s}
It appears that :focus is specified twice for input, textarea, and select;
does this have a particular function?