require "rexml/document"   ;include REXML

 @Skeleton = <<EOF
<anItem desc=""></anItem >
EOF

someItems= REXML::Document.new(@Skeleton)
# Then you could add an/some elements:
# Iterate here
someItems.elements['//anItem'].text = "someThing"


 @drTransactionFile = File.open( "someXML.xml", "w")
 @drTransactionFile.write("<topLevel >" << someItems.to_s <<
"</topLevel >");  @drTransactionFile.close

Not necessarily fast, maybe simple, doubtfully best.

MarkT