So a typical scenario might be to create a virtual in your Ffenics form derived from the ID value (or to add a 'layout only field' to an aspect), place this field on the screen, and refer to its 'value' property in the script.
You don't necessarily want the actual data to appear to the user, so somehow you have to style it so that it is not visible, and scrunch it up in a corner somewhere to keep it out of range of the things you actually want the user to see. If it overlaps with visible objects, it may partially obscure them. And because you have set it to look like it is not there, it's hard to spot it when in designer view.
And you can give such objects a 'hidden field' style that, in designer view, makes them totally obvious (give them a nice bright red background, why don't you) so you can spot them when you're building your wonderful aspect, safe in the knowledge that they will be forever invisible to the user.