mid function
ACTION: returns part of string1 at position with length
USE: string=mid string1, position, length 'if length is omitted then the rest of string1 is returned
EXAMPLE:
s=mid "abcdef",3 : t=mid "abcdef",3,2

RESULT:
s="cdef" : t="cd"

REMARKS: also works with untyped pointers

RELATED: left ltrim rtrim instr mid command