Trying to understand element selection limitations

I have created an ExtendScript which is used to install structured application definitions the first time that a script is run. Here's what it does:

1. Opens a copy of a structapps.fm file that contains the required XML application definitions.
2. Creates a backup of the local structapps file.
3. Opens the local structapps file.
4. Delete any XML applications with names that match the new XML apps.
5. Copies the new XML apps into the local structapps file.
6. Reads the structapps file using fmDispatcher, saves and closes the files.

This all works very well up to a point. Where I have a problem is with the insertion point for the copied XML applications. I want to insert them directly after the <Version> element.

I can do that when there are other following <XMLApplication> elements. However if there are no following elements it inserts the copied elements before the <Version> element which is invalid. Here's the code:

function copyXApps(localStrappDoc, sourceStrappDoc)
{    var copyApps, ser = new ElementRange(), ter = new ElementRange(), copyApps, target,    sourceElem = sourceStrappDoc.MainFlowInDoc.HighestLevelElement.FirstChildElement.NextSiblingElement;    target = localStrappDoc.MainFlowInDoc.HighestLevelElement.FirstChildElement.NextSiblingElement;       if(sourceElem === null || sourceElem.ObjectValid() === false) return;           ser.beg.parent = ser.end.parent = sourceElem.ParentElement;        ser.beg.child = sourceElem;        ser.end.child = sourceElem.ParentElement.LastChildElement;               ser.end.parent = sourceElem.ParentElement;        ser.beg.offset = 0;        ser.end.offset = 0;           //Set the document element selection.    sourceStrappDoc.ElementSelection = ser;    copyApps = sourceStrappDoc.Copy (0);       if (copyApps === Constants.FE_Success){        ter.beg.parent = ter.end.parent = target.ParentElement;        ter.beg.child = ter.end.child = target;        ter.beg.offset = ter.end.offset = 0;               //Set insertion point for copied Xapps, then paste:        localStrappDoc.ElementSelection = ter;        pasteApps = localStrappDoc.Paste (0);        return pasteApps;       }    }

There's also a problem with the selection code which selects all apps except the last one despite using LastChildElement. I seem to be misunderstanding something here.

Thanks for any help.

Ian