Adds rule to a filter that allows files based on a custom callback function. The bitfield needed which is passed in provides information about what sorts of information that the filter function needs; this allows GTK+ to avoid retrieving expensive information when it isn’t needed by the filter.
bitfield of flags indicating the information that the custom filter function needs.
callback function; if the function returns TRUE, then the file will be displayed.
data to pass to func
function to call to free data when it is no longer needed.