Names that begin [Xx][Mm][Ll]

Hi,

we had discussion about reserved names starting with [Xx][Mm][Ll] during
TPAC face-to-face. Main reason was that in recent time I have came
across several usages of such named elements.

Purpose of this email to get feedback about issue from people not
attending face-to-face. Main points of discussion are captured in
minutes available at
http://lists.w3.org/Archives/Public/public-xml-core-wg/2012Oct/0059.html

There are several issues related to such names:

1. Wrong statement about source of reserved names in XML Rec
============================================================

XML Rec says that: "Names beginning with the string "xml", or with any
string which would match (('X'|'x') ('M'|'m') ('L'|'l')), are reserved
for standardization in this or future versions of this specification."

However examples like xml-stylesheet, xml-model or even XML namespaces
(xmlns:...) prove that reserved names are usually defined in separate
specification. On F2F there was consensus to adjust wording and say

"... in this or future specifications from the XML Core WG or its
successors"

If there is agreement about such change, we yet have to find best way
how to implement this change (erratum, new edition, ...).

2. No guidance how to deal with names that are starting with xml
================================================================

In past same XML parsers emitted warning when they came across
element/attribute/PI which was starting with [Xx][Mm][Ll]. However
majority of tools simply doesn't care. This is problem especially in
applications like XML schema editors -- they are not indicating that
such name is wrong.

This might be caused by the fact that XML Rec is not giving enough
guidenance in this regard.

Should spec explicitly say that usage of reserved name has to be reported?

Should all application report this only those who are producing XML or
XML schemas?

Is that practical as list of reserved names can evolve over the time and
not all software component are updated regularly?s

3. Are local names starting with [Xx][Mm][Ll] allowed
=====================================================

We haven't touched this during F2F, but it is related issues.
For example the following two formats are using reserved names for local
names:

http://www.loc.gov/standards/mets/docs/mets.v1-9.html#xmlData

http://blogs.msdn.com/b/ericwhite/archive/2008/09/29/the-flat-opc-format.aspx

We got similar inquiry year and half ago, see thread:

http://lists.w3.org/Archives/Public/public-xml-core-wg/2011May/0007.html

I think that there was no single and clear conclusion whether xml is
reserved when used as a start of local name on element with prefix, like:

<foo:xmlData xmlns:foo="bar"/>

It's probably clear that default namespaces can't be used in this case:

<xmlData xmlns="bar"/>

Some clarification or guidence could be added into XML Names Rec.

4. Should we release reservation of names starting with [Xx][Mm][Ll]
====================================================================

There are documents out which are using reserved names already. We can
choose two ways how to deal with this:

a) Such names were always reserved, it's not our problem, it's your
fault. We might only give more guidenance as outlined above.

b) Since we have namespaces there is no further need to reserve names
starting with [Xx][Mm][Ll]. We can use prefix xml: for future reserved
elements and attributes and prefix xml- for future processing
instructions. We will allow names starting with [Xx][Mm][Ll] with the
exception of xml: and xml-. Advantage of this approach is that we would
decrease divergence between XML Rec and reality.

Any thoughts welcomed.

     Jirka

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