Merge XML documents together overwriting certain elements

[J0StrikE]

I have a 2 input xml files. A template xml file eg\[code\]<test> <a>0</a> <b>0</b> <c>0</c> <d>0</d> <e>0</e></test>\[/code\]and a data xml file that specifies values overriding those in the template xml. The data xml file may not specify values for all elements in the template xml eg\[code\]<test> <a>1</a> <b>2</b> <c>3</c></test>\[/code\]or \[code\]<test> <e>5</e></test>\[/code\]The final xml should be superimpostion of the data xml over the template xml. eg\[code\]<test> <a>1</a> <b>2</b> <c>3</c> <d>0</d> <e>0</e></test>\[/code\]or\[code\]<test> <a>0</a> <b>0</b> <c>0</c> <d>0</d> <e>5</e></test>\[/code\]How can this be done with XSLT?