'System expansion' rewrite

Continuing the all-site re-write, we've re-written and expanded category 13 System expansion.

The original multiple systems concept remains; that page is now much simplified.

Two new pages have been added.

Expand an area

When you need a bit lot more room in the middle, you can expand an area. Use this when the usually-useful Johnny.Decimal constraints get in your way.

Extend the end

And if you just need a bit more room at the end, extend the end. Use this when you just have the odd ID here and there that needs a bit more space.

All the information is on those pages so I'll just let you head over there and read them.

Feedback always welcome. Head to the forum, Discord, or drop me an email.