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Proposals (was Re: The "splice" call)

From: Ray Whitmer <ray@corel.com>
Date: Wed, 20 May 1998 17:25:16 -0600
Message-ID: <3563665C.2F05A747@corel.com>
To: Mike Champion <mcc@arbortext.com>, www-dom@w3.org
Mike Champion wrote:

> Could you elaborate, and perhaps make a more concrete suggestion?
> This
> sounds reasonable ...

Here are 5 suggestions:

1.  Moving the Text.splice() method to a higher-level API than
w3.dom.core, and make it operate on a Node instead of on a Text.

The DOM has two distinct classes of Node, which are perhaps not
sufficiently isolated by the API.  Nodes with string data (Text, PI, and
Comment), and Nodes with child nodes.  In the former case the integer
arguments in the splice call would continue to refer to characters.  In
the latter case, the count would refer to child nodes.

In this higher-level API, I would also include the inverse of splice
(unsplice()?) which removes the specified Element making his children
into siblings of the Node's original siblings.

2.  Provide character position markers.

Iterators are useful to hold positions in a hierarchy which may shift.
The characters of a Text, Comment, or PI node may shift just like
children in the Node hierarchy shift.  For example, I need to hold the
location in a text the user is typing into.  If some other operation
inserts or removes something in the text before my current location, I
want the location I am typing into to be preserved.

A solution would be to add the method getCharPos(int pos) to Node which
returns a CharPos object with a single readable/writable property "pos",
which  is fixed up when character insertions and deletions occur.

i.e.
public interface CharPos()
{
    int getPos();
    int setPos();
}

The Text.replace effect on CharPos inside a replace range is clarified
by specifying that with respect to CharPos it is just a convenience
routine for delete followed by insert.  And null is returned by
getCharPos on anything besides a Text, Comment, or PI.

3.  Complete the random access for Iterators.

It is difficult to create a NodeIterator to hold a known position in the
hierarchy because the iterator is obtained from the parent and requires
traversing to the desired node.

Adding "getChildNumber()" to Node (perhaps with the same performance
note as on "NodeIterator.moveTo(int n)") would allow you to use moveTo
to position an iterator more directly.

Or alternatively add a method "getSiblings()" to a node which
automatically starts a child iterator of the parent at the current node.

4.  Remember relative orders between coinciding NodeIterator or
above-proposed CharPos objects.

When these position holder objects are registered with a containing node
a registration list is often used, in which case an order between
coinciding NodeIterator or CharPos objects can be derived at little
additional cost.

Three enabling additions could be made to the spec, which would not
affect the current DOM behavior if they were not used:

a.  Clarification that the order of coinciding position objects can be
significant.
b.  Ability to specifically reorder coinciding position objects after
traversal
c.  Ability to relatively adjust which way position coinciding objects
shift during insertion

For example:

(a) NodeIterators and CharPos's preserve their original order even when
all intervening Nodes or characters are removed.

(b) The owner of a repositioned NodeIterator or CharPos manually
controls the order via new methods:

property String behavior;
String getCoincidingBehavior()
passCoinciding()

(c) after an insertion, the NodeIterator or CharPos used to position the
insertion shifts any following coinciding positions via a new method:

shiftRelative(int insertionCount, boolean follow)

Currently NodeIterator or CharPos objects precede a coinciding
insertion.  shiftRelative would navigates coinciding NodeIterator or
CharPos objects which follow the current one past the insertion.  If
"follow" is true.

In this case, I believe the benefit is worth the cost of adding these
new methods to NodeIterator and CharPos.

5.  Provide Node.clone() to efficiently copy a sub-hierarchy for
synchronization, replication, and other purposes.

To wrap this up, suggestions (2) - (5) are essential features I need in
a DOM so I can do rather basic things.

I could implement these features as extensions in a private DOM
implementation which implements with the w3 API.

But if I do, I will not be able to employ anyone else's DOM (although
anyone else could plug into mine), because (2) - (5) don't seem to be
easily built from w3 API calls as (1) is.

I have more suggestions relating to good DOM change listener models, but
I guess that waits until later :-).

Ray Whitmer
ray@corel.com
Received on Wednesday, 20 May 1998 19:25:16 GMT

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