my $is_number = qr/^
                   [+-]?                             # optional sign
                   (                                 # then:
                   \d{1,3}(\,\d\d\d)+(\.(\d+)?)?     # n,nnn.nn
                   |\d+\.\d+                         # n.n
                   |\d+\.                            # n.
                   |\.\d+                            # .n
                   |\d+                              # n
                  )
                   ([eE][+-]?\d+)?                   # optional exponent
                   $/xo;