int Ns_SetIUnique( Ns_Set *set, char *key );
Ns_SetIUnique returns 1 if the specified key is unique in the specified set and 0 if it is not. The test for uniqueness is performed case-insensitively. The case-sensitive counterpart to this function is Ns_SetUnique.
For example, a client could send multiple "Accept:" headers which would end up in the header set for the connection. Ns_SetIUnique would then return 0 for the header set and the "Accept" key, because there are multiple fields with the key "Accept".