Returns the name of the order which opened the position.
PosBack- a numerical expression, specifying the number of trade (zero-based).
- 0 - open position;
- 1 - one position back (the last position closed);
- 2 - two positions back, etc.
PosBack is not specified, a value for the open position will be returned.
will return a value of "buy LE" for the last closed position, if this position was opened by the order with "buy LE" name.