Logic to impose a maximum number of checked inputs (two in this demo).
var warning = $(".message");
$("select").multiselect({
header: "Choose only TWO items!",
click: function(e){
if( $(this).multiselect("widget").find("input:checked").length > 2 ){
warning.addClass("error").removeClass("success").html("You can only check two checkboxes!");
return false;
} else {
warning.addClass("success").removeClass("error").html("Check a few boxes.");
}
}
});