code: function flatten(keys) {
    var result = []
    var index = -1
    var length = keys.length
  
    while (++index < length) {
      if (own.call(alias, keys[index])) {
        result = result.concat(flatten(alias[keys[index]]))
      } else if (Array.isArray(keys[index])) {
        result = result.concat(keys[index])
      } else {
        result.push(keys[index])
      }
    }
  
    return result
  }
docs: /* Flatten facial parts.