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Re: TreeWalker.whatToShow

From: Dieter Köhler <dieter.koehler@ppp.uni-bamberg.de>
Date: Sun, 27 Feb 2000 22:02:22 +0100
Message-ID: <38B990DE.6D4E3898@ppp.uni-bamberg.de>
To: keshlam@us.ibm.com, "www-dom@w3.org" <www-dom@w3.org>
> Unfortunately that would defeat the use cases that whatToShow was designed
> to handle, such as "hide the EntityReference nodes".

You are right:  I was more concerned about using TreeWalker.whatToShow
on element nodes.  But to form a judgment on what to do with
EntityReference nodes, I am in need of a clear understanding, whether
the child list of an EntityReference node should be regarded as part
of the document tree.  The DOM 2 draft reads: "... if such an
[corresponding] Entity exists, then the child list of the
EntityReference node is in general the same as that of the Entity
node." So if we have a document like this:

...
<!ENTITY h "hallo">
...
hallo
<a>&h;</a>" 
...

and we set the whatToShow flag to SHOW_ALL, the resulting structure
when applying a TreeWalker seems to be (A):

[Text node: hallo]
[Element node: a]
  [EntityReference node: h]
    [Text node: hallo]

And if we switch of SHOW_ENTITY reference it is (B):

[Text node: hallo]
[Element node: a]
  [Text node: hallo]

But we cannot achieve a result as (C):

[Text node: hallo]
[Element node: a]
  [EntityReference node: h]

without using a filter in a TreeWalker, and we cannot achieve it with
a NodeIterator at all, though it would be the desired output if we are
planning to write e.g. an XML editor.

It seems as if EntityReference nodes need a special treatment, which
is not surprising since the treatment of EntityReferences marks
exactly the difference between a source code view of an XML document
and a browser view before applying style information.  So I would
suggest (if it is to less time to decide now, then for DOM Level 3)
introducing a new flag both to NodeIterators and TreeWalkers called
resolveReferences, which has according to the three different
behavioral patterns A, B, and C (see above) three possible values:
'resolve', 'replace', and 'pure'.  You might ask: why not using a
filter?  My reply would be, a) that especially B and C are standard
cases.  B for XML browsers and C for XML editors.  Therefore we need a
convenient and fast way to implement all these document views in the
DOM. And b), that I can see no way to achieve such a view as C with a
NodeIterator.

So if we have a resolveReferences flag in the DOM, is there any longer
a need for the skip behavior of TreeWalker.whatToShow instead of the
reject behavior?

> ... You can write the desired filtering behavior today. The question is whether
> the current behavior is excessively confusing even when documented.

My question is, which of both behavioral patterns is the best way to
get the desired results.  Therefore I discussed some different
examples of use for iterators, since I hope that my thoughts might
help to make a good work a little better.

> >And finally, a suggestion for an additional attribute for the
> >NodeIterator and TreeWalker interface:
> >    filtered of type boolean
> 
> How would this differ from, eg, (NodeIterator.getFilter()!=null)?

What I had in mind was the question, what would be the most elegant
way to switch a filter off and on again in an object orientated
programing language.  If we do it your way, the applications has to be
aware of the filter that was attached to an iterator before it was
switched off; if we do it the way, I suggested, the information stays
with the iterator, which seems to be closer to the philosophy of
object orientated programing.  BTW: I borrowed this idea from the
treatment of iterating database tables in Delphi.

-- 
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Received on Sunday, 27 February 2000 16:05:03 GMT

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