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Re: [xml-dev] Generic XML Tag Closer </> (GXTC)

On Fri, Aug 18, 2006 at 04:31:34PM +0800, Melvin Chin wrote:
> May I seek some opinions on this topic/proposal?
> To extend XML spec just a little to permit use of "</>" (GXTC)

One of the reasons we took this out of XML (it was in SGML, of
course) was that we knew from a decade (roughly) of implementation
experience that there were some problems with it.

The most common problem was people losking track of tags, and
thinking they had closed something they hadn't.  Sometimes they
would get an error and spend ages trying to fix it.  A program
that filled in the close tags would (as they saw it) "do the
wrong thing", and they'd even file bug reports, at SoftQuad we
got bug reports about minimization on a regular basis even
though the problem was always (OK, once someone found a real
bug, so almost always) though it was the data that was faulty.

When there was no error, the markup was incorrect.

And sometimes the frustrated people trying to correct the error
would just shove end tags in there until the thing parsed :-)

With a LISP program,
    (multiply (3 (add 4 7) 6))
    (multiply (3 (add 4 7 6)))
are both syntacitcally valid, but when you run them you get different

With XML, people were marking up assertions about text, precisely
because the computer couldn't do it.  You can't "run" a document
to tell if a title has got an extra line of text in it by mistake,
or that you've marked up an author's name as "Aerial Photography",
to quote an example mentioned at Extreme Markup.  A human looks
at the metadata and says, "this is poor quality", but the
computer is perfecrly happy.

If you really want to try it MSXML on Windows supports it via
the API, there's a flag you can turn on.  But you would be
creating documents that were not XML and that you could not share,
that would break existing tools.

The supposed benefit of minimisation -- and there are a host of
other similar features -- is for people typing XML "by hand",
e.g. on a card punch.  For automatically generated XMl there is
no real benefit -- the extra few bytes help in debugging and
robustness, and vanish when compression is used.

But it turns out that the minimisation features can actively
hinder people what ALan Cooper called the "perpetual intermediate",
the user who doesn't type XML all day long, but does it at least
often enough to know some of the features.  These users are often
the ones who drive adoption the most strongly.

So no, I don't think it's a good improvement, although I do get
asked about it maybe once a month.



Liam Quin, W3C XML Activity Lead, http://www.w3.org/People/Quin/
http://www.holoweb.net/~liam/ * http://www.fromoldbooks.org/

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