When the display is called, it will be called either with a set of explicitly specified parameters, or a parameter file. Take a couple of steps back and try to work out what calls the display up (if it's FTView ME, it'll be a GoTo Display button of some sort).
Open the configuration dialog for that control, and you'll see that it specifies not only the display to open, but also a parameter file or just a simple list of parameters. If it's a parameter file, open it up and you'll see something like:
Code:
#1=SomeTag
#2=SomeOtherTag
#3=Retro_Encabulator
That tells you that when this display is called, every instance of #1 will be replaced with SomeTag, every instance of #2 will be replaced with SomeOtherTag, and so on.
If they've not specified a parameter file, but just listed the parameters directly, then the first listed parameter is #1, the second is #2, and so on. All separated by commas.
The reason this is (generally) done is so that you can create one generic display to show multiple instances of an object. E.g. you can build a valve control popup, and pass the specific valve UDT or AOI to the display as parameter #1. Then you just map the open button to #1.OpenPB, and at runtime it'll evaluate as The_Valve_I_Clicked_On.OpenPB (or whatever).
