zero suppression vs compression in addresses

[michael.dillon at bt.com]

> Input parsers need to understand every possible 
> representation, as long as it's syntactically correct.  This 
> draft doesn't change what is to be considered a syntactically 
> correct representation, so for a *reader*, it is just not 
> very relevant.

People have been saying that a double colon can appear
once and only once in an IPv6 address. If you write code
that will only accept a single occurence of double colon
and it meets one of these canonical IPv6 addresses, then
it won't work.

So, this draft *DOES* change what is considered to be
a syntactically correct when it allows "::" to be used
twice. Admittedly, section 4.2.3 is not very clear and
it may not survive future discussion, but the bulk of
this draft is very clear and well-reasoned. It is worth
reading by anyone who is working on code that converts
between IPv6 binary and text representations. Regardless
of its status, the recommendation to output text addresses
using only lowercase abcdef is a good one.

--Michael Dillon