Re: [IANA #1275238] URN:NAN registration request

Overall, I approve of this application.  There are a few details that I
think could be improved.

1. There are two uses of "SHOULD" in the text:

    A colon SHOULD be used within the prefix only as a delimiting
    character between the ISO 3166-1 country code and sub-namespace
    code(s), which splits the national namespace into smaller parts.

    A hyphen SHOULD be used as the delimiting character between the
    prefix and the NAN string.  Within the NAN string, a hyphen MAY be
    used for separating different sections of the identifier from one
    another.

However, both of these statements are implied by the BNF, and the BNF is
implicitly "MUST", so the meaning is better captured by changing
"SHOULD" to "MUST".

2. This statement is correct in its general meaning but I think the
wording is not quite correct:

    URN:NAN syntax is equivalent to the URN:NBN syntax.

"equivalent to" usually means that the two sets of BNF define exactly
the same thing.  "parallel to" or "similar to" might be better.

3. In regard to case handling, the following statements are made:

    prefix      = iso-cc *( ":" subspc )
                ; The entire prefix is case insensitive.

    The structure (if any) of the NAN_string is determined by the
    authority for the prefix. Whereas the prefix is regarded as case
    insensitive, NAN strings can be case sensitive at the preference of
    the assigning authority; parsers therefore MUST treat these as case
    sensitive, and any case mapping needed to introduce case
    insensitivity is the responsibility of the relevant resolution
    system.

    Note that because case mapping for ASCII letters is completely
    reversible and does not lose information, the case used in
    case-insensitive matching is a local matter.  Implementations can
    convert to lower or upper case as they see fit; they only need to do
    it consistently.

The first two statements are completely clear and appear to be exactly
correct.  But I think the third statement is inconsistent with the first
two.  And also, case mapping, in the form of mapping letters of both
cases to one case, *does* lose information.  I suspect that the third
statement is left over from an early version of the NBN template and
should be omitted.

4. John asks "What is the difference between an NBN and an NAN?"  It may
be that librarians and archivists conceptualize a difference between the
two sets of objects even if from an informatics point of view they are
identical.  In any case, this is a matter for "Community
Considerations".

Dale