Syntax:     POS(find str,source str[,n])

Defn: A CI evaluator function that finds the nth occurrence
of specified string in a source string, beginning either
from the left (when n is positive) or the right (when n
is negative).

Type: Integer

Example: pos('ab','cgabd')
Result: 3

Example: pos('b','abcbe',2)
Result: 4

Example: pos('b','abcbe',-1)
Result: 4