Why cant xml:id be numeric only ?

First off I know asking "Why" for anything standards related is silly.

But given that, could anyone give me a rationale or history for restricting xml:id (or the ID type from DTD) to be NCName which then has to start with non-numeric ?

It seems such an *obvious* (to me!) concept that an ID could be fully numeric like   xml:id="12345".

Why force it to start with a letter  like  xml:id="a123" (or a DTD or schema ID value'd attribute like  id="12345" )

I know I can fairly easily add such a letter, then hack all the queries to prepend the letter ... but I'm very curious why the constraint ?  I would guess a great deal of ID's 'in the wild' are purely numeric.

Use Case: Why I'm asking is that I have a large number of documents which are effectively dumps from a database.

Each element has a 'natural ID' which is the integer primary key from the database.

I'm trying to optimize XQuery & xslt to use the built-in indexing in common engines which supports "ID" values via  fn:id() and have discovered to my surprise I simply cant use numeric values for an ID.  Quite curious.

-David

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David A. Lee

dlee@...

http://www.xmlsh.org

Thanks,  I suspected something from the distant SGML land as it seems entrenched in the DTD history ..

But obviously any sane person would assume

                xml:id="D000001"   == xml:id="D1"

:) 1/2

On 29/04/2011 15:22, David Lee wrote:

First off I know asking "Why" for anything standards related is silly.

But given that, could anyone give me a rationale or history for restricting xml:id (or the ID type from DTD) to be NCName which then has to start with non-numeric ?

I seem to recall asking this once, and being told that the history lay in the SGML rules for abbreviated syntax. Something like allowing <e id="xyz"/> to be abbreviated as <e xyz>. Not that this in itself would make a numeric identifier ambiguous, but it would account for requiring an ID value to have the same syntax as an attribute name.

I guess another justification is that it prevents any debate about whether xml:id="01234" is a duplicate of xml:id="1234".

Michael Kay
Saxonica