It's really already very much like you want it to be. Most Str objects do not in fact have any byte semantics. If you say "foo".bytes, that is shorthand for "foo".bytes(:nf<c>, :enc<UTF-8>). In other words, you have to tell it what units you want the bytes to be measured in. It just assumes utf-8 as a convenient default. Likewise a Str does not have any codepoint semantics unless you tell it the normalization to assume. Most strings are sequences of abstract graphemes; see also http://www.nntp.perl.org/group/perl.perl6.language/2008/01/msg28281.html as well as the recent definitions of .bytes, .codes, .graphs, and .chars in http://svn.pugscode.org/pugs/docs/Perl6/Spec/Functions.pod .
We do still talk about the possibility of multi-level strings, but that's basically the same as your object that presents both Str and Buf interfaces. That's an exception rather than the rule, and certainly as you say it would need to be well typed as to its encoding and normalization. The same considerations apply between grapheme and codepoint views of the same string, except there only the normalization is needed, since codepoints are above the encoding abstraction level. Larry
