I don't understand undo.History

Question

My expectation for app.undoHistory was that anything I can undo in the UI is listed in that array.
This does not seem to be the case.
In my current tests the only way I find to get
b anything
into that array is the script "FindChangeByList.jsx". No action and no script of mine add anything undoable, it seems.
That makes me suspect that I lack some elementary piece of understanding...
What gives?
Thank you
Gerald

Answer 1

Thank you Shane,
thinks: I see my second post before Shane's answer although it was written later. Weird.
For those interested, this seems to work rather nicely:
var anUndoStack = app.activeDocument.undoHistory;
anUndoStack.splice(40);
var anUndoName = app.activeDocument.undoName;
var myDialog = app.dialogs.add({name:"An Seite ausrichten"});
with(myDialog.dialogColumns.add()){
var myUndoDropdown = dropdowns.add({stringList:anUndoStack, selectedIndex:0});
var myResult = myDialog.show();
if(myResult == true){
var mySteps = myUndoDropdown.selectedIndex;
myDialog.destroy();
for (n= 0; n<mySteps;n++) { app.activeDocument.undo(); }
} else{
myDialog.destroy();