docs: function createdDate(key, value, prop) {
    var val = prop ? get(value, prop) : value;
    var str = val || key;
  
    var re = /^(\d{4})-(\d{2})-(\d{2})/;
    var m = re.exec(str);
    if (!m) return null;
    return String(m[1]) + String(m[2]) + String(m[3]);
  }