Behavior differences in operator[] object creation with a json_pointer

Discussed in https://github.com/nlohmann/json/discussions/5356

^{Originally posted by samcmill August 3, 2026}
The following code throws a parse_error.106 exception due to the 01 token.

#include <iostream>
#include <nlohmann/json.hpp>

using json = nlohmann::json;

int main() {
    json obj = json::object();

    auto ptr = json::json_pointer("/a/b/01/d"); 

#ifdef INIT
    obj[json::json_pointer("/a/b")] = json::object();
#endif

    obj[ptr] = "value";

    std::cout << obj << std::endl; // prints {"a":{"b":{"01":{"d":"value"}}}}
}

However, if the first part of the JSON object up to 01 is pre-initialized, then the '01' token is treated as a string and the code runs successfully.

1. Is this expected behavior? It seems unintuitive to me. Regardless, I am currently taking advantage of this behavior by walking the json_pointer and pre-initializing to handle cases like this.
2. Would it make sense to have a mode where all json_pointer tokens are always treated as strings?

Related: #4446

Start with the json_pointer overload of operator[] and the linked discussion, then reproduce the sample with and without INIT to compare token handling. Trace how the /01 token is interpreted during object creation. Done should include a documented resolution of the behavior and tests for both initialization paths, with any string-token mode explicitly scoped.