code: function radio(bind, el, param, value) {
    var group = element('span', {'class': RadioClass});
  
    el.appendChild(group);
  
    bind.elements = param.options.map(function(option) {
      var id = OptionClass + param.signal + '-' + option;
  
      var attr = {
        id:    id,
        type:  'radio',
        name:  param.signal,
        value: option
      };
      if (valuesEqual(option, value)) attr.checked = true;
  
      var input = element('input', attr);
  
      input.addEventListener('change', function() {
        bind.update(option);
      });
  
      group.appendChild(input);
      group.appendChild(element('label', {'for': id}, option+''));
  
      return input;
    });
  
    bind.set = function(value) {
      var nodes = bind.elements,
          i = 0,
          n = nodes.length;
      for (; i<n; ++i) {
        if (valuesEqual(nodes[i].value, value)) nodes[i].checked = true;
      }
    };
  }
docs: Generates a radio button group.