This particular expert advisor contains a very useful code which is often required by the developers. Most of the time , we need the last active trade. But in this EA you can search a trade with any index.
By active trade ,I mean market orders not pending orders
if you pass 0 then it will fetch the most recent active trade
If you pass 1 then it will fetch the trade before that and so on.
We can filter the trades based on symbol and magic number.