bug#3687: 23.1.50; inconsistency in multibyte eight-bit regexps [PATCH]

[Eli Zaretskii <eliz@gnu.org>]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Fri, 28 Jun 2019 16:05:07 +0200
> Cc: mituharu@math.s.chiba-u.ac.jp, monnier@iro.umontreal.ca,
>         3687@debbugs.gnu.org
> 
> > 1. What do you mean by "raw bytes"?  Is #xab a raw byte or a Unicode
> >    point U+00AB?  IOW, how do we distinguish, in a regexp, between a
> >    raw byte and a character whose Unicode codepoint is that byte's
> >    value?  And how does one go about concocting a regexp that matches
> >    raw bytes in a unibyte or multibyte buffer or string?
> 
> Sorry, I should have been more clear. The terminology in the manual is a bit muddled; in this case I mean the characters (or whatever you prefer calling them) obtained with hex or octal escapes in the range 128-255, such as "\xff" or "\377", regardless of the string's type (unibyte or multibyte).
> 
> Unicode characters in the range 128-255 can be generated using the \u00HH or \U000000HH notations, or by just including them literally. They are distinct from raw bytes.
> 
> To match raw bytes, just write them. They are not special in regexp syntax and need no escaping.

And one more question about this part: if hex and octal escapes are
reserved for raw bytes, then what is \123456 and its ilk, i.e. octal
escapes whose values are above 255 decimal?  Are they errors to be
signaled about?