.feedback question

.feedback {
color: #ccc;
text-align: right;
clear: all;
}
When I used the CSS Validator on w3.org, it stated that the “clear: all;” line is invalid because “all” is not supported by CSS but only HTML. This is the only line that produces an error in my code. Can I just delete this line of code? Change it? Is it even useful, and if so, what does it do? Thanks.