c_gtk_file_filter_add_custom

Undocumented in source but is binding to C. You might be able to learn more by searching the web for its name.
__gshared extern (C)
void function(GtkFileFilter* filter, GtkFileFilterFlags needed, GtkFileFilterFunc func, void* data, GDestroyNotify notify) c_gtk_file_filter_add_custom;

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