What DLL is player.transform.position.x from?

Code:

var bumFights = {
    Title : "BumFights",
    Author : "Brimstone",
    Version : V(0,1,0),
    Description : "Let's spawn some people in and give them weapons",
    HasConfig : false,
   
    Init: function (){
        command.AddChatCommand('findme', this.Plugin, 'Smile');
        },
    Smile: function (player)
    {
            rust.SendChatMessage(player, "bumFights", player.transform.position.x, "0");
            rust.SendChatMessage(player, "bumFights", player.transform.position.y, "0");
            rust.SendChatMessage(player, "bumFights", player.transform.position.z, "0");
    },
}

If you type /findme on my server you get the proper coords but I am not sure why that works or where to look this command up. Any ideas?

 

Assembly-CSharp.dll

 

But the actual class, transform etc comes from UnityEngine.dll