data to lookup
the GSequenceIterCompare function used to compare iterators in the sequence. It is called with two iterators pointing into seq. It should return 0 if the iterators are equal, a negative value if the first iterator comes before the second, and a positive value if the second iterator comes before the first.
user data passed to iter_cmp
an GSequenceIter pointing to the position of the first item found equal to data according to cmp_func and cmp_data.
Like g_sequence_lookup(), but uses a GSequenceIterCompareFunc instead of a GCompareDataFunc as the compare function. Since 2.28