Not referring to toppings, but to working stuff into the meat.
I was brought up in the School of Unadulterated Beef, but I read a lot of recipes where people (especially in restaurants) put stuff in there, like butter, shallots, herbs, A1, foie gras, Worcestershire, whatever.
Is this common? Is your standard burger an Amalgamation? Was this your innovation, or something Ma and Pa did too?
The truth is that regular burgers bore me, so I never eat them anymore.