> If id="1" were missing from 1.XML should it be deleted from 2.xml?
> If id="2" in 2.xml contained the word 'kosmos' should it contain 'world'
> after the merge because it was replaced by id="2" from 1.xml?
> In the real world is t a complex element if so do you intend to merge the
> contents of ts of the same id from each xml file or simply replace the t 
> in
> 2.xml with the one in 1.xml?

Yes i cant simly replace beacuse in one file node with id="2" can have 
"Hello"
in second file id="2" may have "Hallo"

I try to explain little bit more :=

file 1.xml is a "template" file, containing strings/texts in native 
language(Estonian)
With my application users can translate strings to they own language.
When now user launches translator application

1) template is loaded from server
2) application checks if template file contains new id's(nodes) and adds 
those nodes to user file.


[template.xml]
<test>
    <t id="1">Tere</t>
    <t id="2">Maailm</t>
    <t id="3">Head aega!</t>
</test>

[user.xml]
<test>
    <t id="1">Hallo</t>
    <t id="2">World</t>
</test>


After synchronizing user.xml must look like this
<test>
    <t id="1">Hello</t>
    <t id="2">World</t>
    <t id="3">Head aega!</t>
</test>




Meelis