+ /* Checks if the specified name is a valid user/group name. Also see POSIX IEEE Std 1003.1-2008, 2016 Edition,
+ * 3.437. We are a bit stricter here however. Specifically we deviate from POSIX rules:
+ *
+ * - We don't allow any dots (this would break chown syntax which permits dots as user/group name separator)
+ * - We require that names fit into the appropriate utmp field
+ * - We don't allow empty user names
+ *
+ * Note that other systems are even more restrictive, and don't permit underscores or uppercase characters.
+ */