code: function getImmediateCustomParentTag(tag) {
    var ptag = tag;
    while (ptag.__.isAnonymous) {
      if (!ptag.parent) { break }
      ptag = ptag.parent;
    }
    return ptag
  }
docs: Loop backward all the parents tree to detect the first custom parent tag
  @param   { Object } tag - a Tag instance
  @returns { Object } the instance of the first custom parent tag found