Re: The <any/> element: bane of security or savior of versioni

>It's also perfectly reasonable, and often useful, to suggest that such additional content is to be stored

> along with other data
 

Completely agree. Indeed in some circumstances there may be a mandatory audit step that occurs before stripping any content such that in the future the message received can be accurately recovered by both sender and receiver such as in the case of non repudiation.
 

On 22/10/2007, noah_mendelsohn@u... <noah_mendelsohn@u... > wrote:

For what it's worth, I've slowly come to believe that the general case for
forwards compatibility is not necessarily that new content is completely
ignored by older applications, but that there be some default rule for
dealing with it.  "Must ignore" is just one example of such a rule.  It's
also perfectly reasonable, and often useful, to suggest that such
additional content is to be stored along with other data, perhaps that it
is to be printed using some default formatting rules, etc.  Note that in
HTML as currently deployed, even elements not named explicitly in the
spec, say <banana>, can be styled using CSS.   One point of view is that
HTML+CSS therefore contains all such elements in its language.  Another is
that <banana> is extension content, but with the rule that it still shows
up in the DOM, still is scriptable, still can be styled via CSS, etc.  So,
I've come around to the view that Must Ignore is just an extreme case of a
default processing rule.  Note that if your very first step in receiving a
V2 message in a V1 processor is to strip out everything that's new, you
can't do things like digital signatures on it.   So my suggestion is that
for forwards compatibility, early versions of a language need a very well
chosen default processing (or default interpretation) rule:  whether the
best rule is Must Ignore, and whether the rule can be implemented by a
transform will depend on the circumstances and the requirements.

Noah

--------------------------------------
Noah Mendelsohn
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
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