Interoperability of Content Management System

Hi.
In the comparison table (http://cmsmatrix.org/), there are several criteria:

Content Syndication (RSS)
FTP Support
UTF-8 Support
WAI Compliant
WebDAV Support
XHTML Compliant
What are they?
What are their uses?
Which one is important, which one is not?
Which one is necessary to have, which one is not where substitute can be found elsewhere?

Thanks.