текстовый редактор (text editor)
Входные файлы (Input files)
Input files shall be text files or files that would be text files
except for an incomplete last line that is not longer than
{LINE_MAX}-1 bytes in length and contains no NUL characters. By
default, any incomplete last line shall be treated as if it had a
trailing <newline>. The editing of other forms of files may
optionally be allowed by ex implementations.
The .exrc files and source files shall be text files consisting
of ex commands; see the EXTENDED DESCRIPTION section.
By default, the editor shall read lines from the files to be
edited without interpreting any of those lines as any form of
editor command.
