SOA serial rotation

[Sam Wilson]

Can anyone provide a current reference showing how to recover from a
mistakenly high value of the SOA serial number?  I'm sure there used to
be good web pages about it but I can't find them any more.  The RFC
describing sequence space numbering doesn't actually give any examples
of what it's useful for!

(It's for someone else.  Yes, I could write a description myself but it
wouldn't be as good as descriptions I remember reading elsewhere.) 

Sam