code: function checkbox(bind, el, param, value) {
    var attr = {type: 'checkbox', name: param.signal};
    if (value) attr.checked = true;
    var node = element('input', attr);
  
    el.appendChild(node);
  
    node.addEventListener('change', function() {
      bind.update(node.checked);
    });
  
    bind.elements = [node];
    bind.set = function(value) { node.checked = !!value || null; }
  }
docs: Generates a checkbox input element.