>>-lastPos(needle-+--------+-)---------------------------------><
                  +-,start-+

Returns the position of the last occurrence of a string, needle, in the receiving buffer. (See also Section 5.4.15.25, “pos”.) It returns 0 if needle is the null string or not found. By default, the search starts at the last character of the receiving buffer and scans backward. You can override this by specifying start, the point at which the backward scan starts. The start must be a positive whole number and defaults to receiving_buffer~length if larger than that value or omitted.

x1 - .mutablebuffer~new("abc def ghi")
x1~lastPos(" ")      ->    8
x1 - .mutablebuffer~new("abcdefghi")
x1~lastPos(" ") -> 0
x1 - .mutablebuffer~new("efgxyz")
x1~lastPos("xy")     ->    4
x1 - .mutablebuffer~new("abc def ghi")
x1~lastPos(" ",7) -> 4