Confusion while implementing the DOM.

Miles Sabin msabin at
Wed Jun 2 13:55:24 BST 1999

Andrew Douglas wrote,
> <root>
>   <elone>Hello</elone>
>   <eltwo>Goodbye</eltwo>
>   <elone>Gutten Adbend</elone>
>   <eltwo>Aufwiedersehen</eltwo>
>  </root>
> My underlying structure looks like this
>                         opentag(root)
>                            |
>                        zomcontent
>                |-----------+-----------------|
>            sequence                      sequence
>         |------+-----|                |------+-------|       
> opentag(elone) opentag(eltwo) opentag(elone) opentag(eltwo)
>       |               |              |             |   
>     text            text           text          text
> Not suprisingly, it looks like a tree!  So, all these 
> things can be Nodes, but not all are Elements (opentags 
> are) -- some are probably DocumentFragments(zomcontent, 
> sequence, ...).
> So, my DOM implementation has the usual first/last
> Child, getChildNodes, get Next/Previous siblings, and 
> so on, but sometimes these children aren't Elements, 
> but are DocumentFragements.

Ahh ... no, I'm afraid that's not quite right. The DOMs
idea of the structure of your document would be,

  Document doc
    Element root          == doc.getDocumentElement()
      Element elone       == root.getFirstChild()
        Text Hello        == elone.getFirstChild()
      Element eltwo       == elone.getNextSibling()
        Text Goodbye
      Element elone
        Text Gutten Adbend
      Element eltwo
        Text Aufwiedersehen

A Document *never* has a DocumentFragment amongst its
children: the latter exist solely to provide a 
lightweight holder for Nodes which are _owned_by_, but 
not _part_of_ a given Document.

Note that all Nodes that are created on a particular
Document (eg. via Document.createElement()) are always
owned by that Document (and so can't be pasted into a
different doc), but don't become part of it until they're
explicitly added (eg., via someNode.appendChild()).

I hope that helps a bit ...



Miles Sabin                          Cromwell Media
Internet Systems Architect           5/6 Glenthorne Mews
+44 (0)181 410 2230                  London, W6 0LJ
msabin at           England

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