How does the "<param>_?" work in json files in mOS?


I started using this format that I coped from an example forWiFi configuration and tried it in a few different places with varied success.

In WiFi AP mode I use it like this and it sets the _?????? to a six digits that I’m guessing are from the chip ID or something.

    "wifi": {
        "ap": {
            "enable": true,
            "ssid": "esp32_??????",
            "pass": "",
            "trigger_on_gpio": -1

The one I’ve found most interesting is with device id. Using the below format in my conf1.json file

    "device": {
        "id": "esp32_??????"

And magically I see my actual device ID being set in conf9.json. Not sure how the magic happens or where it’s documented but would be nice to know what works and what doesn’t.

For example I tried the same for come GCP and AWS stuff and it didn’t work there, but works in the above.

Any tips or links to docs would be appreciated.