On Monday, August 30, 2021 at 4:06:34 AM UTC+2 John MacFarlane wrote:
When the attribute syntax was introduced, the decision was made
to require that identifiers start with a letter. (…) This applies both to autogenerated and explicitly given ids.
Thanks for clarifying this.
Thanks @Saku Laesvuori for the workaround using `{id=123}`.