/^
   [+-]?         # first, match an optional sign
   (             # then match integers or f.p. mantissas:
       \d+\.\d+  # mantissa of the form a.b
      |\d+\.     # mantissa of the form a.
      |\.\d+     # mantissa of the form .b
      |\d+       # integer of the form a
   )
   ( [eE] [+-]? \d+ )?  # finally, optionally match an exponent
$/x;