to be (perhaps part of) the "invisible" characters in a prompt, or the
required prompt character which follows the literal sequence (this character
must be one with a printing column width >= 1). The literal indicator
character (which is just a marker, and not printed anywhere) (the PSlit
parameter in sh(1)) can also be a wide char (passed to libedit as a wchar_t,
encoded as that by sh(1) or other applications that support this.)
Note: this has currently only been tested with everything ascii (C locale).