$ perl5.12.2 junk
Compiling REx "-?\p{Nd}{1}"
Final program:
   1: CURLY {0,1} (5)
   3:   EXACT <-> (0)
   5: CURLY {1,1} (19)
   7:   ANYOF[{unicode}+utf8::Nd] (0)
  19: END (0)
minlen 1
Matching REx "-?\p{Nd}{1}" against "1"
   0 <> <1>                  |  1:CURLY {0,1}(5)
                                  EXACT <-> can match 0 times out of 1...
   0 <> <1>                  |  5:  CURLY {1,1}(19)
                                    ANYOF[{unicode}0-9...+utf8::Nd] can match 1 times out of 1...
   1 <1> <>                  | 19:    END(0)
Match successful!
Matches
Freeing REx: "-?\p{Nd}{1}"