Over the years I’ve collected a rather messy ~/.ssh/config which resulted in some undesired behavior as a result of me misunderstanding how the config file prioritizes its options.

Today I investigated that.
In short, this is what I found:

Priority goes from top to bottom
Defaults MUST come last
Host specificity is NOT a factor of priority
Host sections can be specified multiple times
Multiple hostnames (and aliases) may be specified per section
Host sections apply to the name you use (not what it resolves to)