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In an XML form document, the XForm models which you can add to the
document support a new property called "Model data updates change
document's modification status".

This property can be controlled in the "Add Model" resp. "Edit Model"
dialog, where it is offered as check box.

If ON, then changes you do to form controls bound to any data in the
model will set the document to modified.
If OFF (the old and still default behavior), then changes to such
control's data will not mark the document as modified, which means the
"Save" button remains disabled (if it was before the control data change).

The specification at
http://specs.openoffice.org/appwide/xforms/GUI_spec_part1.sxw has been
adjusted.