'True if the document has been modified since it was loaded or since
the last time is_modified was set to False.'

@dynamic_property
def is_modified(self):

    def fget(self):
        return self.document().isModified()
    def fset(self, val):
        self.document().setModified(bool(val))
    return property(fget=fget, fset=fset)
