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### 28.5 Terminal Parameters

Each terminal has a list of associated parameters. These terminal parameters are mostly a convenient way of storage for terminal-local variables, but some terminal parameters have a special meaning.

This section describes functions to read and change the parameter values of a terminal. They all accept as their argument either a terminal or a frame; the latter means use that frame’s terminal. An argument of `nil` means the selected frame’s terminal.

Function: terminal-parameters &optional terminal

  This function returns an alist listing all the parameters of terminal and their values.

Function: terminal-parameter terminal parameter

  This function returns the value of the parameter parameter (a symbol) of terminal. If terminal has no setting for parameter, this function returns `nil`.

Function: set-terminal-parameter terminal parameter value

  This function sets the parameter parameter of terminal to the specified value, and returns the previous value of that parameter.

Here’s a list of a few terminal parameters that have a special meaning:

`background-mode`

  The classification of the terminal’s background color, either `light` or `dark`.

`normal-erase-is-backspace`

  Value is either 1 or 0, depending on whether `normal-erase-is-backspace-mode` is turned on or off on this terminal. See DEL Does Not Delete in The Emacs Manual.

`terminal-initted`

  After the terminal is initialized, this is set to the terminal-specific initialization function.

`tty-mode-set-strings`

  When present, a list of strings containing escape sequences that Emacs will output while configuring a tty for rendering. Emacs emits these strings only when configuring a terminal: if you want to enable a mode on a terminal that is already active (for example, while in `tty-setup-hook`), explicitly output the necessary escape sequence using `send-string-to-terminal` in addition to adding the sequence to `tty-mode-set-strings`.

`tty-mode-reset-strings`

  When present, a list of strings that undo the effects of the strings in `tty-mode-set-strings`. Emacs emits these strings when exiting, deleting a terminal, or suspending itself.

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