Towards the bottom, it says the following:
A wild card is a particular card, often a joker, which can be used to substitute for any card the holder wishes, even a duplicate of a card the holder already has. Several cards may be designated as wild - for example all the twos. This must be agreed in advance.
The hand ranking
is the same as described above, except that it is now possible to have five of a kind - five cards of the same rank - in which of course at least one will be represented by a wild card. Five of a kind is the highest combination, beating a Royal Flush.
I don't know if this is the most reliable, but this is what I found.