Consider using string without spaces for braille code metadata

[bertfrees]

IMO using a string without spaces for the braille code metadata would make more sense.

• It is more intuitive: people associate unique identifiers with things without spaces: UUID, ISBN, product serial numbers, ...
• We would preserve compatibility with other standards, such as URN, and BCP 47 language tags. For instance, this would keep the possibility open to integrate the braille code in a language tag, using the "T" or "X" extension (or maybe even the variant subtag), as was discussed here.