текстовый редактор (text editor)
Последствия ошибок (Consequences of errors)
When any error is encountered and the standard input is not a
terminal device file, ex shall not write the file or return to
command or text input mode, and shall terminate with a non-zero
exit status.
Otherwise, when an unrecoverable error is encountered, it shall
be equivalent to a SIGHUP asynchronous event.
Otherwise, when an error is encountered, the editor shall behave
as specified in Command Line Parsing in ex.
The following sections are informative.
