A Telnet SubOption to send to the server with the SubOption command.
async setDoSubOption(doSubOption: Uint8Array): void;
For a list of valid Telnet suboptions and their descriptions please look at the Telnet RFCs.
You don't need to specify the suboption start and suboption end codes. Those are appended automatically by the class. For example, to send a terminal type suboption to request setting the terminal type to 'vt100', you must send ASCII 24, followed by ASCII 0, followed by "vt100" (without the quotes).
This property is write-only and not available at design time.