Readonly Characters Are a Big Deal

Summary

Readonly Characters Are a Big Deal Nov 10, 2025 I like Emacs UX as exemplified by Magit. I consider it to be a user interface paradigm on the same footing as UNIX pipes: An Engine for an Editor Pipes give you 1D read-only streams of characters which excel at batch processing. Emacs is all about interactive mutable 2D buffers of attributed text. Today I realized that an important feature of Emacs text buffers is read-only characters (manual). Like in any editor, you can mark an entire Emacs buffer as read-only. But you also can mark individual substrings read-only, so that you can edit anywhere except specific ranges This is a useful feature for bidirectional interaction. Consider the in-editor terminal I am using currently, which looks like this: ./zig/zig build fuzz -- message_bus = time: 3s = info(fuzz): Fuzz seed = 2355780251053186744 info(message_bus_fuzz): command weight: reserved = 0 info(message_bus_fuzz): command weight: ping = 0 info(message_bus_fuzz): command weight: pong = 0 info(message_bus_fuzz): command weight: ping_client = 0 info(message_bus_fuzz): command weight: pong_client = 0 info(message_bus_fuzz): command weight: request = 0 info(message_bus_fuzz): command weight: prepare = 37 info(message_bus_fuzz): command weight: prepare_ok = 0 The first line is the command to execute, this is typed by me manually, and then I hit a “submit” shortcut to actually run the command. Then goes the status line, which shows how long the command has been running so far and the exit code (when the command terminates). The status line is determined by the “terminal” itself. Finally, there’s output of the command itself, updated live. In this sort of the interface, command is modifiable by the user, but is read-only for the editor. Status is the opposite — the editor updates it every second, but the user should be prevented from touching it. And the output can be CRDT-style edited by both parties (I often find it useful to edit the output in place before pasting it else...