What programs can ask for

A program talks to the terminal in escape sequences mixed into its output. Most of them move the cursor or change a color, and JediTerm handles those. A few ask the terminal itself for something: open this link, copy this text, tell me when you are done. Termina honors these, within limits, because the program asking may be on the far side of an ssh and its output is whatever it chose to print.

Declared links (OSC 8)

ls --hyperlink, compilers and gh can mark text as a link to somewhere else. Ctrl+click (Cmd+click on macOS) opens it like any other link, and with the modifier held a line at the bottom of the pane shows where it really goes, since the text can say anything. Only the schemes a link in the text may use are accepted, so a javascript: target is not a link. See Links.

The clipboard (OSC 52)

A program can put text on the clipboard. This is how vim and tmux copy across SSH, where the program has no other way to reach your machine’s clipboard.

• Write only. A program can never read the clipboard. Answering would hand whatever was last copied, passwords and tokens included, to anything that asked, including a program on another machine.
• Only text. Data that is not valid base64 or not UTF-8 is dropped rather than put on the clipboard garbled.
• Settings → Terminal → Input → Let programs copy to the clipboard (on by default) turns writing off too.

Notifications (OSC 9, OSC 777)

A program can post a notification, such as a build saying it has finished. Both common forms are read:

printf '\e]777;notify;Build;done\a'   # urxvt's, which foot, kitty and WezTerm read too
printf '\e]9;done\a'                  # iTerm2's

• The tab is marked with a magenta dot, which outranks the bell’s yellow and the activity mark’s cyan, in the theme’s own rendering of each. A tab you are looking at is not marked.
• It reaches the desktop unless you are looking at that pane: the window in front, the tab selected and the pane active. On Linux it goes through notify-send, or straight to the session bus with gdbus where notify-send is not installed; on macOS through osascript; on Windows as a PowerShell toast. A notification with no title is titled after its tab.
• One per pane every two seconds reaches the desktop, so a loop printing OSC 9 cannot fill the screen with bubbles. Every one still marks the tab.
• The text is treated as hostile. Control characters are stripped, the title and the message are cut to a length a bubble can show, and they reach each command as an argument or an environment variable, never inside a script.
• Not every OSC 9 is a notification. ConEmu numbers subcommands under it (9;4 is a progress bar, 9;9 a directory), and those are not posted.
• Settings → Terminal → Display → Desktop notifications (on by default) turns the desktop half off. The tab is marked either way.

The directory (OSC 7)

A shell can report its working directory, as a file:// URI. On Linux and macOS Termina ignores the report and asks the operating system instead, which works whatever your prompt does, and which a shell inside ssh cannot claim for another machine’s path.

On Windows the operating system is asked too: the directory is read out of the shell process. But a WSL tab’s process is wsl.exe, whose directory says nothing about where the Linux shell inside it is, so there a directory the shell reports wins. The same holds for a program started as bash.exe, which is how Git Bash runs. Both OSC 7 and ConEmu’s OSC 9;9, the form PowerShell and Command Prompt send when set up for Windows Terminal, are read, and only for a directory on this machine that exists. A tab with a directory opens new tabs there and turns relative paths into links.

Prompt marks (OSC 133)

A shell that marks where its prompts and commands begin and end gets Previous Prompt and Next Prompt, Select Last Output, and a red bar beside a command that failed. See Search and prompts, which has the lines to add to bash and zsh.

The kitty keyboard protocol

In a terminal, several keys send the same bytes as others: Escape is the start of every escape sequence, Ctrl+I is Tab, and Shift+Enter is Enter. A program can ask for the kitty keyboard protocol to tell them apart, and Termina implements all of it. Neovim, Vim, Helix, fish and nushell ask by themselves.

• The first flag gives unambiguous keys: Escape on its own, Ctrl+I apart from Tab, and Shift+Enter as a key of its own.
• The further flags add repeats and releases, the shifted key, every key including the modifiers, and the text each key types.
• Nothing changes for a program that does not ask. Every key keeps its usual bytes. Under the first flag plain typing, Enter, Tab and Backspace keep them too, so reset can still be typed after a program that crashed with the protocol on. reset clears it.
• Each screen keeps its own mode, so an editor on the alternate screen can change it without disturbing the shell’s, and a program’s query is answered.

Three things are approximated, because JavaFX does not report them: a right-hand modifier is reported as the left one, the optional base-layout key is never sent, and AltGr is told apart from Ctrl+Alt by whether the press composed a character.

Type-ahead over slow SSH

While ssh is the program running in the tab and the far end is slow to echo, what you type appears at once, dimmed and underlined until the echo confirms it, and the cursor moves ahead with it.

• JediTerm’s predictor decides when. It measures the delay, learns what echoes, notices a password prompt, and backs off when it guesses wrong. It shows nothing until the median echo takes longer than 100 ms, so on a fast link it stays out of the way.
• A local shell is never predicted. It echoes within a frame, and a prediction there could only ever be wrong.
• Settings → Terminal → Input → Predict typing over slow SSH (on by default) turns it off.