Yes, I misread that when implementing restrictions on DNS labels as well (answering with a different RFC from a sibling): "The DNS itself places only one restriction on the particular labels that can be used to identify resource records. That one restriction relates to the length of the label and the full name." -- https://tools.ietf.org/html/rfc2181#section-11

Also, to get a full view of DNS, the HTML view of the RFC links to all the updates to DNS over the years: https://tools.ietf.org/html/rfc1035

Which is pretty handy.