ZMODEM, XMODEM and YMODEM
File transfer inside the terminal stream, for serial lines and legacy gear.
Some devices only move files through the terminal itself.
ZMODEM
A transfer starts when the remote sz or rz begins. Motty takes the stream from
the screen, shows a progress dialog, and returns the terminal to normal when it
ends.
XMODEM and YMODEM
These protocols never announce themselves in the stream, so you start them from the terminal's menu, choose the protocol (XMODEM checksum, CRC or 1K, or YMODEM batch) and the direction, and start the program on the other side yourself. After that the transfer behaves like a ZMODEM one.
What a peer cannot do
Everything from the other end is treated as hostile. A file name is reduced to a plain name, a size claim allocates nothing, and the peer cannot choose a path or make Motty run a command.