Provide a formal definition of what characters are allowed in the FQBN

[kittaakos]

Describe the request

Is there a formal definition of what characters are allowed in the FQBN? I am looking for something similar to the sketch file and folder names spec. I found a related entry in the FAQs: What’s the FQBN string? (but it does not answer the question: #1236) and the {build.fqbn} section in the platform spec:

the FQBN (fully qualified board name) of the board being compiled for. The FQBN follows the format:
VENDOR:ARCHITECTURE:BOARD_ID[:MENU_ID=OPTION_ID[,MENU2_ID=OPTION_ID ...]]

Is there a regex or a grammar with the vendor, architecture, etc. terminals? Thank you!

Describe the current behavior

I did not find a spec for the FQBN

Arduino CLI version

76ea8c1

Operating system

N/A

Operating system version

n/a

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the nightly build
• My request contains all necessary details