code: function getTag(dom) {
    return dom.tagName && __tagImpl[getAttr(dom, RIOT_TAG) || dom.tagName.toLowerCase()]
  }
docs: Detect the tag implementation by a DOM node
  @param   { Object } dom - DOM node we need to parse to get its tag implementation
  @returns { Object } it returns an object containing the implementation of a custom tag (template and boot function)