Mathematica indicates for the user to define it later.  An error.

In[3]:= Permutations[{1,2},{-2}]

Permutations::nninfseq: 
   Position 2 of Permutations[{1, 2}, {-2}]
     must be All, Infinity, a non-negative integer, or a List whose 
first
     element (required) is a non-negative integer, second element 
(optional)
     is a non-negative integer or Infinity, and third element (optional) 
is a
     nonzero integer.

Out[4]= Permutations[{1, 2}, {-2}]