The zsh/clone Module
====================
The zsh/clone module makes available one builtin command:
clone TTY
Creates a forked instance of the current shell, attached to the
specified TTY. In the new shell, the PID, PPID and TTY special
parameters are changed appropriately. $! is set to zero in the new
shell, and to the new shell's PID in the original shell.
The return value of the builtin is zero in both shells if
successful, and non-zero on error.