The POSIX specification of vi
Certain terminals do not have all the capabilities necessary to support the complete vi definition. When these commands cannot be supported on such terminals, this condition shall not produce an error message such as "not an editor command" or report a syntax error. The implementation may either accept the commands and produce results on the screen that are the result of an unsuccessful attempt to meet the requirements of this volume of POSIX.1-2024 or report an error describing the terminal-rel