Escape codes and conventions for semantic marking of
commands (as in shells and other REPLs) and their components
(prompts, user inputs, and output).
# Motivation
The user interaction in shells and other [REPL applications](https://en.wikipedia.org/wiki/Read-eval-print loop) is a sequence of commands,
where each _command_ is a sequence of _user input_ (one or more lines typed by the user) and command output (from the application).
The input lines will usually contain _prompt_ sections emitted
by the application, usually at the beginning of the first line.
This protocal defines a way for an application to specify to a terminal
the start and end of commands and their parts: input, promp, and output.
This can enable useful features like visual separation/highlighting
of commands; folding (a button to hide long command output);
searching or copying of command input or output; or indication of return status.
This specification is an extension of the protocol
first implemented by [FinalTerm](https://github.com/p-e-w/finalterm) and
then later by [iterm2](https://iterm2.com/documentation-shell-integration.html).
Other similar prior art is known for
[Extraterm](http://extraterm.org/) and [DomTerm](http://domterm.org/Wire-byte-protocol.html).
# Detail
A command sequence may be nested withing the output section of
another command, for example when the user types a shell command
to invoke some other REPL application. To help track this
nesting we make use of an optional _application identifier_ (`aid`)
which can be an arbirary string specified by the application.
It is suggested that the `aid` be (or contain) the process id of the
application; if that is unavailable, the name of the application.
## Commands
`OSC "133;F\007"`
> Do a _fresh-line_: If the cursor is the initial column
> (left, assuming left-to-right writing), do nothing.
> Otherwise, do the equivalent of `"\r\n"`.
`OSC "133;A"` _options_ `"\007"`
> First do a _fresh-line_.
> Then start a new command, beginning with the prompt.
`OSC "133;E"` _options_ `"\007"`
> Same as `OSC "133;A"` but may first implicitly terminate a previous command:
> If the _options_ specify an `aid` and there is an active (open)
> command with matching `aid`, finish the innermost such command
> (as well as any other commands nested more deeply).
> Otherwise, treat as an `aid` whose value is the empty string.
`OSC "133;P"` _options_ `"\007"`
> Start of secondary prompt. This is used for multi-line prompts,
> right-side prompts, and prompts for continuation lines.
`OSC "133;B"` _options_ `"\007"`
> End of prompt and start of user input, terminated
> by a `OSC "133;C"`.
`OSC "133;I"` _options_ `"\007"`
> End of prompt and start of user input, terminated
> by end-of-line.
`OSC "133;C"` _options_ `"\007"`
> End of input, and start of output.
`OSC "133;D"`[`";"` _exit-code_]_options_`"\007"`
> End of current command.
> The optional _exit-code_ is an integer value that reports
> an exit code from the command. This should be a non-negative integer,
> where 0 means successful completion, and non-zero for failure.
## General options syntax
Options have the general format:
> _options_ ::= (`";"` _option_)*
In general, an _option_ can be any string of characters not including control characters (value less than 32) or semicolon. Usually the will have the form of a _named-option_:
_named-option_ ::= _option-name_ `"="` _value_
A terminal must ignore an _option_ whose _option-name_ it doesn't recognize.
**Issue**: Alternative specification: If a terminal doesn't recognize an _option-name_ it should ignore it _and_ any subsequernt options.
**Issue**: Maybe allow _value_ to be a quoted string, with C-style escapes?
## Standard options
`aid=` _value_
> The current _application identifier_.
`click-move=` _value_
> The _value_ can be `line` or other options to be determined later.
> This is a request from the application to the terminal to
> translate clicks in the input area to cursor movement.
