how does Sketch determine the latest version?
sparkle:version property is set for each version listed in your appcast.
Sketch parses all the version strings and determines the latest version from that.
0.0.1 is less than 0.1 is less than 1
We use the same code in Sketch so even if we released a "45.2" after release "46", then "46" would be seen as the latest version.
what date-time format should I use for the pubDate property?
The pubDate property is currently not used. The same goes for the channel/link url.
can we use raw markdown in the descriptions instead of html?
We have not modified in anyway how Sparkle parses the Appcast file and at present have no intention of doing so.
This means that you need to keep to the Sparkle format. We currently don't use this information.
Currently we only use a small subset of the information defined by the creators of Sparkle in the Appcast.
You just need the list of items (updates) and for each item you just need to specify the enclosure with the version and the download url defined. Currently anything else is ignored.