The behavior I wanted using jQuery is:
HTML
<input class="chkRelevance" type="checkbox" id="chkRel1" />
<label for="chkRel1">Relevant</label>
<span> </span>
<input class="chkRelevance" type="checkbox" id="chkRel0" />
<label for="chkRel0">Not Relevant</label>
JS
$(".chkRelevance").on('click', function (event) {
var me = $(this),
meChecked = me.prop('checked'),
idx = parseInt(me.attr('id').substr(6)),
other = $('#chkRel' + (idx ^ 1));
if (meChecked && other.prop('checked')) {
other.prop('checked', false);
}
});