[amonrabr]

Strings are letters, you cant use math here...
Arrays, you can use more numbers, example: a={1,2,3...} if 5 is in a, do...
this.thing... It just has the number when you are online, when you reconnect you will lose this number.. example: this.a=1; if (this.a==1){do...} this flag just can be loaded in this npc. If a different npc has the same line, this.a=1; they are 2 differents numbers...
if you have 2 npcs in the same level, and you want that they are the same, you can use "level.thing"