The reason I ask is that I originally thought QBE went up on close with significant volume (a very good sign, but I only had a quick look at yahoo page). However, after checking the proper order history, I realize that most of this volume was actually lower than the close price (though above what I paid) as special crossings.
How are these events initiated? Do X and Y independently go to broker and say I want to buy / sell significant holding and then broker negotiates a price? I assume it is done so as to not influence price unduly.