def chars_until str
      slice_str = @str.check_until(Regexp.new(Regexp.escape(str)))
      return chars_left unless slice_str
      return slice_str.size - str.size
    end
def chars_until str
      slice_str = @str.check_until(Regexp.new(Regexp.escape(str)))
      return chars_left unless slice_str
      return slice_str.size - str.size
    end
Returns how many chars there are between current position and the
 string given. If the string given doesn't occur in the source, then
 the remaining chars (#chars_left) are returned.

 @return [Fixnum] count of chars until str or #chars_left