The Confluce import documentation says:
Confluence OnDemand can only import spaces that are exported from a Confluence instance of the same major version
So I thought I could use UWC to generate a confluence export file. But the TWiki information from UWC says:
You don't need an exporter to get the TWiki page data.
The converter works from the source data files on the file system.
Alas... Is there any way to migrate a Twiki instaince to Confluence OnDemand?