Re: First strawman for UTF-8 headers proposal

[Keith Moore <moore@xxxxxxxxxx>]

On Saturday, November 29, 2003, at 03:43  PM, Paul Hoffman / IMC wrote:

> One thing I didn't say in the first message, which I probably should 
> have, is that it is a fairly-obvious extension of 8BITMIME. All the 
> lessons we have learned in the past decade (!) from 8BITMIME should be 
> applied with whatever I propose here.

I'm not sure how much the 8BITMIME experience applies.  At the time 
8BITMIME was adopted, the Internet was much smaller, there were many 
fewer UAs, MTAs, and other mail-handling tools (and thus less variety), 
messages travelled a simpler path (fewer firewalls, spam filters, virus 
checkers, etc.) and the vast majority of Internet users still spoke 
English - though this was quickly changing.

Also, 8BITMIME was a much less drastic change than negotiation of UTF-8 
would be now.  Partially this is because many mail readers in use at 
the time of 8BITMIME introduction were still intended for use with text 
terminals or terminal emulators (so MUAs that copied 8bit text to the 
screen often "did the right thing" even if only by accident, or because 
the user had configured the terminal emulator to use the right 
charset).  Partially this is because MTAs and other intermediaries that 
predated 8BITMIME generally did not look at message bodies - they 
looked only at the headers of messages that transited their systems,.  
Since headers of 8bit MIME messages are still ASCII supporting 8BITMIME 
didn't necessarily require any change to a tool's header-parsing code.

One simple example.  Bernstein and others have pointed out that it's 
easier to parse header fields with address lists from the right to the 
left rather than from the left to the right, because this requires less 
lookahead.  It's still possible to do this with UTF-8 (particularly if 
you do lexical analysis left-to-right and parsing right-to-left), but 
it's probably not a trivial change to existing code.