The filter change cannot be described with any of the other enumeration values.
The filter is less strict than it was before: All items that it used to return %TRUE for still return %TRUE, others now may, too.
The filter is more strict than it was before: All items that it used to return %FALSE for still return %FALSE, others now may, too.
Describes changes in a filter in more detail and allows objects using the filter to optimize refiltering items.
If you are writing an implementation and are not sure which value to pass, %GTK_FILTER_CHANGE_DIFFERENT is always a correct choice.