Hyphen Restrictions

[John C Klensin]

--On Wednesday, January 05, 2011 15:18 +0900 Yoshiro YONEYA
<yoshiro.yoneya at jprs.co.jp> wrote:

> Hi, all,
> 
> I need clarification of RFC5891 section 4.2.3.1, which says:
> 
> 4.2.3.1.  Hyphen Restrictions
> 
>    The Unicode string MUST NOT contain "--" (two consecutive
> hyphens) in    the third and fourth character positions and
> MUST NOT start or end    with a "-" (hyphen).
> 
> My question is that what "the third and fourth character
> positions" means. Does it mean third and fourth octet from the
> beginning of the string? For example:
>   beginning of the string
>     |
>     v 1   2   3   4   5 <-- position of octet
>     +---+---+---+---+---+
>     | a | b | - | - | c |
>     +---+---+---+---+---+
>               ^   ^
>               |   |
>       two consecutive hyphens
>...
> 
> My understanding for this restrictions is to preserve future
> ACE prefix,  so I expect the answer for my question is former
> one.  Is that right?

Yes

   john