As diff3x is an XML representation we here consider going one step further and making use of the fact that the representation is hierarchical to support hierarchical or 'nested' change. A nested change is a change in one branch that modifies something that has been removed in another branch.

We will look at an XML example, showing nested changes.

<author>
<personname>
 <first>Nigel</first>
 <last>Whitaker</last>
</personname>
<address>
 <ph>01684 532141</ph>
 <st>Geraldine Rd</st>
 <city>Malvern</city>
 <country>UK</country>
 <post>WR14 3SZ</post>
</address>
</author>

<author>
<personname>
 <first>Nigel</first>
 <last>Whitaker</last>
</personname>
<address>
    
 <st>Geraldine Rd</st>
 <city>Malvern</city>
 <country>UK</country>
 <post>WR14 3SZ</post>
</address>
</author>

<author>
<personname>
 <first>Nigel</first>
 <last>Whitaker</last>
</personname>







</author>

In the above example one branch, B.xml, has deleted the address sub-tree which the other branch has modified with an added phone number. As we are now using an XML representation that has a tree structure we can also make use of this structure in the result.

In order to distinguish between a simple <ao> option and a nested choice, we introduce the <aoChoice> element. This is a mixed content element that can include <a> or <o> elements as well as text.

<d:diff3x a="A.xml" b="B.xml" o="O.xml"><![CDATA[
<author>
<personname>
 <first>Nigel</first>
 <last>Whitaker</last>
</personname>]]>
<d:choice3>
 <d:aoChoice include="true"><![CDATA[
   <address>]]>
     <d:a><![CDATA[
      <ph>+44 1684 532141</ph>]]>
     </d:a>
    <![CDATA[
    <st>Geraldine Rd</st>
    <city>Malvern</city>
    <country>UK</country>
    <post>WR14 3SZ</post>
   </address>]]>
  </d:aoChoice>
  <d:bChoice/>
 </d:choice3><![CDATA[
</author>]]>
</d:diff3x>

Here we can see that by allowing nested change we can avoid the repetition and make it easier for a human to understand. However, in order to support this in the format we have to introduce quite a number of new elements and different rules. This adds to the complexity of the format and moves us a lot further away from the original elegant simplicity of diff3. Keeping diff3x as simple as possible seems preferable to including the ability to represent a subset of changes as nested changes.

For this reason we have elected not to include the ability to represent nested changes in diff3x.