Update
Add expression:ItemCnt, Keys2ItemCnt to get item count.
For example, hash = {"a":10,"b":20}
Hash.ItemCnt("") will return 2 (key = "" means root)
Hash.ItemCnt("a") will return 1
The assignment of key for mutildimation is the same as expression:Hash.At , Hash.AtKeys --
Hash.ItemCnt("a.b.c")
Hash.Keys2ItemCnt("a","b","c")