For an intensely interactive application such as a text editor, performance is part of "make it work". If the screen is lagging behind keypresses, or trivial c

For an intensely interactive application such as a text editor, performance is part of "make it work". If the screen is lagging behind keypresses, or trivial commands (e.g. the mentioned reordering of tabs) take long enough to wonder whether the program is hung, the basic contract of user interface has been broken. Basing the core of a text editor (not only scripting, as in Emacs, but input, rendering, event handling, data structures) on low-performance technology is as wrong as, say, designing it for single-byte character sets only.