An aspect of the X protocol which I never saw anyone take advantage of: the client, not the server, got to pick wire ID #'s. In principle, a simple gui program could've preassigned and hardcoded all its identifiers, letting the server worry about the mapping problem. In practice, it seems like everyone used toolkits such that the X ID was arbitrary, the memory location of the widget was arbitrary, and there needed to be mapping layers between both of those as well as between the widget-in-memory and the widget-description-in-resource-file...