Gosling Emacs was especially notable for its efficient redisplay code, which used a dynamic programming technique to solve the classical string-to-string correction problem. The algorithm was quite sophisticated; that section of the source was headed by a skull and crossbones in ASCII art, warning would-be improvers that even if they thought they understood how the display code worked, they probably did not.
Since Gosling had permitted its unrestricted redistribution, Richard Stallman used some Gosling Emacs code in the initial version of GNU Emacs. UniPress began selling Gosling Emacs (which it renamed Unipress Emacs) as a proprietary product, and, controversially, asked Stallman to stop distributing Gosling Emacs source code. UniPress never took legal action against Stallman or his nascent Free Software Foundation, believing "hobbyists and academics could never produce an Emacs that could compete" with their product. All Gosling Emacs code was removed from GNU Emacs by version 16.56, with the possible exception of a few particularly hairy sections of the display code. Recent versions of GNU Emacs (at least as of August 2004) no longer even contain the "skull and crossbones" warning.