In the the last Litmus conference that I attended in Boston this year, I believe it was brought up that we should no longer be using brackets in our media queries.

For example:

td[class="showMobile"] {
    display: block !important;
    max-height: none !important;

    Instead it should be written:

    .showMobile {
    display: block !important;

Can anyone confirm this? I have tried to google this and I am not getting any recent information.