How is commandArgument passed to onCommand handler?

Hi!
I have simple button on my form with CommandArgument and CommandName set.

<asp:Button ID="Button2" runat="server" CommandName="Order" CommandArgument="IArg" oncommand="Button2_Command"
            Text="Button" />


I have handler for oncommand event:
protected void Button2_Command(object sender, CommandEventArgs e)
    {
        var arg = e.CommandArgument;
    }


I was just wondering how my CommandArgument is passed to that handler...


Here is generated html for the button:
<input type="submit" name="Button2" value="Button" id="Butt ...