Adding use re 'debug'; for m/-?\p{Nd}/ and  m/-?\p{Nd}{1}/ shows 
$ perl5.12.2 junk
Compiling REx "-?\p{Nd}"
synthetic stclass "ANYOF[\-][+utf8::Nd]".
Final program:
   1: CURLY {0,1} (5)
   3:   EXACT <-> (0)
   5: ANYOF[{unicode}+utf8::Nd] (17)
  17: END (0)
stclass ANYOF[\-][+utf8::Nd] minlen 1
Matching REx "-?\p{Nd}" against "1"
Matching stclass ANYOF[\-][+utf8::Nd] against "1" (1 chars)
Contradicts stclass... [regexec_flags]
Match failed
Doesn't match
Freeing REx: "-?\p{Nd}"

[download]
 
$ perl5.14.1 junk
Compiling REx "-?\p{Nd}"
synthetic stclass "ANYOF{i}[\-][{non-utf8-latin1-all}{unicode}{outside
+ bitmap}+utf8::Nd]".
Final program:
   1: CURLY {0,1} (5)
   3:   EXACT <-> (0)
   5: ANYOF[{unicode}{outside bitmap}+utf8::Nd] (16)
  16: END (0)
stclass ANYOF{i}[\-][{non-utf8-latin1-all}{unicode}{outside bitmap}+ut
+f8::Nd] minlen 1
Matching REx "-?\p{Nd}" against "1"
Matching stclass ANYOF{i}[\-][{non-utf8-latin1-all}{unicode}{outside b
+itmap}+utf8::Nd] against "1" (1 bytes)
   0 <> <1>                  |  1:CURLY {0,1}(5)
                                  EXACT <-> can match 0 times out of 1
+...
   0 <> <1>                  |  5:  ANYOF[{unicode}{outside bitmap}0-9
+...+utf8::Nd](16)
   1 <1> <>                  | 16:  END(0)
Match successful!
Matches
Freeing REx: "-?\p{Nd}"

[download]

$ 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] ca
+n match 1 times out of 1...
   1 <1> <>                  | 19:    END(0)
Match successful!
Matches
Freeing REx: "-?\p{Nd}{1}"

[download]
 
$ perl5.14.1 junk
Compiling REx "-?\p{Nd}{1}"
Final program:
   1: CURLY {0,1} (5)
   3:   EXACT <-> (0)
   5: CURLY {1,1} (18)
   7:   ANYOF[{unicode}{outside bitmap}+utf8::Nd] (0)
  18: 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}(18)
                                    ANYOF[{unicode}{outside bitmap}0-9
+...+utf8::Nd] can match 1 times out of 1...
   1 <1> <>                  | 18:    END(0)
Match successful!
Matches
Freeing REx: "-?\p{Nd}{1}"

[download]

In reply to Re^2: Simple regex should match number by Anonymous Monk
in thread Simple regex should match number by Anonymous Monk

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