substr:(string,start,length)
string is the character string to be subdivided
start is the sequence number (starting from the left and
numbered 1,2...) of
the first character to be selected. Default returns a null string.
length is the number of characters to be selected. Default is 'to last
character'.
substr:(ABCD1234,3,4) is replaced by CD12
substr:(ABCD1234,2) is replaced by BCD1234
