code: function mkdux (node, data = {}) {
    if (node instanceof Container)
      node = node.domElement
    node[STARDUX_PRIVATE_ATTR] = ( node[STARDUX_PRIVATE_ATTR] || data )
    return node[STARDUX_PRIVATE_ATTR]
  }
docs: Make stardux data object on a
  node if not already there.
  
  @private
  @param {Object} node
  @param {Object} [data = {}]
  @return {Object}