0 if needle
is a null string or not found. By default, the
search starts at the last character of
haystack and scans backward to the
beginning of the string. You can
override this by specifying
start, the point at which the
backward scan starts and length, the range of
characters to scan. The
start must be a positive whole number and
defaults to the length of haystack if larger than that
value or omitted.
The length must be a non-negative whole
number and defaults to start.