does this script target people who have an item in their bags? or items from mobs?

[SteelBalls]

I was reading wowhead about ways of getting the Phosphorescent Stone Drake which drops off a rare. One trick someone put in to the comments was a script that you had to /say or /w or put in general chat or something and it would tell you if the rare that contained the reins of this mount was active.

So my question is, when I see someone randomly link an item in /say in the auction house for instance and they don't say anything about the item, are they really trying to target someone who has it in their bags? Can the following script be used to target people who have x item in their bags if you just change the main part ("Reins of the phosphorescent Stone Drake") to read the item you want to find?

/script DEFAULT_CHAT_FRAME:AddMessage("Shift-click this to place a link into a chat message: \124cffa335ee\124Hitem:63042:0:0:0:0:0:0:0:0\124h[Reins of the Phosphorescent Stone Drake]\124h\124r");

[JonBoy2001]

I believe it's meant to be used to see if the item has dropped since reset.

[wrathblade]

queries the server for info about that item and if it does it means the item has already dropt.
thus seeing these rares have long respawn timers means it's been looted.

atleast thats how i used it some time ago

[microtonal]

As far as I know, there's no way for you to see what items another player has in their bags. That data simply isn't getting pushed to your client, and there's no reason for it to be.

[huangzhong9]

Well i am fairly certain that you cannot have prior knowledge of what a mob is going to drop before you kill and loot it, as far as checking if a player has the item in their bags, i would say it probably doesn't do that either.

[Odayaka]

The script will show if the item has been registered on the server since reset. That means that if someone has it in their bags, it will register. If the mob spawns and drops the reins and is looted, it registers on the server. If you put the script in and neither of these criteria has been met it hasn't been registered and the item won't show up in chat.

[Deleted]

It's "exploiting" (notice the quotes) a quirk of the way item links are handled on the client. Whenever an item link is clicked, the following are executed:
1. Check the client item cache. If the item is found, use this data. Else,
2. Query the server for item info. If the item is found, use this data. Else,
3. Do nothing.

The server will only return item data for items it has "seen" since the last reset. It will automatically "see" any items dropped in raid instances since sometime in WotLK IIRC (people apparently used it in BT to find instances with Warglaives off Illidan), but otherwise it will only "see" items when a mob has them generated as part of their loot table (or a player has them in their inventory) - thus, if the link printed by the macro does not react to clicks (no tooltip), that means that the server has not "seen" the item since the reset (no player with it has logged on, and the mob dropping it has not spawned yet).
This will only work if your client does not have a cached copy of the item's information, of course.