D likes very much to name or collect things in a series; if he’s going to line up his cars to play “Crossing Gate,” he first gathers them all, then names them all, and only then can he line them up in an orderly way, with one as the designated “driver” or leader. If he can’t remember the name of a new car or old train he’ll say “This..??” Sometimes he’ll now say “what is…” or “who is…” this. Names of things are important but so is their quantity; perhaps one day he will own a fine collection of vintage sports cars.
Here is a sweet example of the naming of things.