[Exim] Definition of header field in Exim?

Hello,

Exim 4.12 defines header fields in src/expand.c:445 as sequence of
characters of

mac_isgraph(*s) && *s != ':'

Said macro is:

#define mac_isgraph(c) \
((uschar)(c) > 32 && (uschar)(c) != 127)

That includes in 8-bit characters.

RFC 2822, section 3.6.8 says:

field-name      =       1*ftext

ftext           =       %d33-57 /               ; Any character except
                        %d59-126                ;  controls, SP, and
                                                ;  ":".

That forbids 8-bit characters. Shouldn't Exim follow the RFC there?

Michael