Confused about mid() command

[1micha.elok]

Perhaps like this one ... ?

Code:

'Console Mode
a = "ABCDEF"

pln "a                  = "+a
pln

'display the letters "B" to "E" inclusive...
b = mid(a,1,4)
pln "MID(a,1,4)         = "+b

'replace D with X
pln "REPLACE D with X   = "+replace(b,"D","X",2)
pln

system "pause"