/^(?:
   0\ but\ true  |
   (?:
      \s*    # leading spaces ignored
      [-+]?  # optional sign
      (?:
         (?i: inf|infinity|nan ) | # any case of inf or nan
         (?: \d+ (?:\.\d*)? | \.\d+ ) # digits, optional .
            (?: [eE] [-+]? \d+ )?     # optional exponent
      )
      \s*    # trailing spaces (including "\n")
   )
  )\z
/x;