This question evaluates proficiency in parsing and traversing deeply nested JSON structures, handling missing keys, distinguishing arrays from objects, extracting specified fields, and comparing recursive versus iterative traversal strategies.
Given a JSON document with approximately five levels of nesting, write code to traverse it and extract specified fields while handling missing keys, arrays vs. objects, and unknown nesting depth. Compare recursive and iterative approaches, discuss complexity, and outline robust error handling and schema validation strategies.