Every statement in a JavaScript program is enclosed in a hierarchy of nested scopes, from which the variables declared there are visible to the statement. The QML debugger currently has no way of exploring those scopes and their members.

Instead we are apparently trying to shoehorn as much scope as possible into the implicit "this" variable by modifying the QML language and setting "this" to whatever object seems convenient at that point. So far this hasn't led to major disaster, but we should really recognize that scopes and "this" are different concepts in JavaScript, and treat them as such in the debugger.