is

An overloaded function that tests for or places a mask.

  bool is(mask m, charT c) const;
  

Test if c matches the mask m.

Returns true if the char c matches mask.

  const charT* is
  (const charT* low, const charT* high,
  mask* vec) const;
  

Fills between the low and high with the mask argument.

Returns the second argument.