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The new third edition of XML inspired me to read through the latest
errata. I have a problem with one of them that I think is a
substantial and unnecessary change to the definition of XML.
E57 states:
Amend the first paragraph after the example declarations so that it reads:
The value "default" signals that applications' default
white-space processing modes are acceptable for this element; the
value "preserve" indicates the intent that applications preserve all
the white space. This declared intent is considered to apply to all
elements within the content of the element where it is specified,
unless [E13]overridden with another instance of the xml:space
attribute. This specification does not give meaning to any value of
xml:space other than "default" and "preserve". It is an error for
other values to be specified; the XML processor MAY report the error
or MAY recover by ignoring the attribute specification or by
reporting the (erroneous) value to the application. Applications may
ignore or reject erroneous values.
Rationale
Although the required behavior was clear when validating, it was
under-specified when not validating. Making it an "error" makes it
clear that "default" and "preserve" are the only blessed values, but
that processors and applications are not obligated to react
drastically.
I disagree with allowing nonvalidating processors to signal any form
of error when encountering xml:space="something else". I think the
previous spec was quite clear that this was not allowed, and that
should not be changed now. Furthermore, in practice, these "maybe
fatal, maybe not" errors are a huge pain in the posterior. They are a
major source of interoperability problems between parsers. They were
a mistake in the first place, and I really, really don't want to see
any new ones blessed in the spec.
With regard to validating processors, the original spec is less
clear. It states:
A special attribute named xml:space may be attached to an element to
signal an intention that in that element, white space should be
preserved by applications. In valid documents, this attribute, like
any other, must be declared if it is used. When declared, it must be
given as an enumerated type whose values are one or both of "default"
and "preserve". For example:
A lot depends on the interpretation of "must" in the last sentence.
In particular, is it a general rule for all declarations are does it
just apply "In valid documents" as in the previous sentence. I prefer
the latter interpretation, which would make it a validity error
rather than a fatal error. Either way though, provided the attribute
is properly declared in the DTD as specified here, I think it is
still well-formed (though not valid) to have xml:space="something
else" in a document parsed by a validating parser. I don't think this
should be changed now.
One final meta-note: I really wish these errata would be publicly
discussed and debated before being snuck out the door in the dead of
night.
--
Elliotte Rusty Harold
elharo@metalab.unc.edu
Effective XML (Addison-Wesley, 2003)
http://www.cafeconleche.org/books/effectivexml
http://www.amazon.com/exec/obidos/ISBN%3D0321150406/ref%3Dnosim/cafeaulaitA
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