What are the rules for de-capitalisation, etc of topic titles?

Immediate adjunct to this topic: Where are the rules for post and message title de-capitalization? I’ve noticed that all caps titles are auto-demoted, presumably to reduce textual shouting. I can all-caps some of the words, just not all.

(Sorry to ask. I’ll launch my own test instance ASAP.)

That is the title prettify setting, which has a few examples in the description: