m/
  ^          # anchor to the beginning of the string
  -?         # 0 or 1 dashes (for negative numbers I assume)
  \.?        # 0 or 1 decimal points
  \d+        # 1 or more numbers
  (?:\.\d+)? # 0 or 1 decimal places followed by a number
  $          # anchor to the end of the string
/x