Usage:
n = INSTR(s1, s2)
Description:
Use INSTR to find a substring within a string.
INSTR returns the 1-based index of the start of s2 within s1.
For example, INSTR("find", "in") returns 2. INSTR returns 0 if the substring was not found.
NOTE: The comparison is case sensitive, which means that INSTR("find", "IN") returns 0.
