function add_tag(tag) {
    $('tags').value += " " + tag;
}
function remove_tag(tag) {
    $('tags').value = $('tags').value.gsub(tag," ");
}

function tag_poem() {
    add_tag("poem");
    remove_tag("shortstory");
    remove_tag("novella");
    remove_tag("novel");
    remove_tag("other");
}
function tag_shortstory() {
    add_tag("shortstory");
    remove_tag("poem");
    remove_tag("novella");
    remove_tag("novel");
    remove_tag("other");
}