You should set this tag to
False whenever you export the contents
of the gadget or overwrite them with something new.
Even if you have set up notification on this tag, you should still get it before you kill the text, because this makes it possible to do some advanced testing to see if the text has actually been modified, e.g. by checking the undo buffer, comparing checksums or checking whether or not the text buffer is empty (none of this is currently done, but it may be in the future).