a question about begin and character encoding

[TXYH1]

Hello, I haven't been able to figure out a few questions. Can you help me?

If it's just to satisfy:

for i := 0; i < len(siblings); i++ {

d. darts.Check [begin+int(siblings[i].code)] = begin

}

Why is the value of begin begin = pos - int (siblings [0]. Code'), based on what consideration? Why not start with 0

And why code = Unicode + 1

Thank you