This question is only regarding aircraft that seat more than about 100 people.
Are cargo holds pressurised these days, what is the situation?
Are only some pressurized, most, of every single one? Does it depend on the carrier, operating region or are there other variations that matter?
Are cargo holds heated?
Do they have lights? (Aren't some lit for animals?)
I've noticed random mentions of "some" of the sections being pressurised. Is this correct? It would seem to me that, if indeed, only some are pressurised then, of course, you absolutely could not rely on your luggage being in a pressurised area.
and what about Fedex-type cargo-only aircraft?
To be clear, I ask this question re "today" because I noticed when googling on this, there is a lot of information, but only old information (say, 10 yrs old plus). That is a recipe for confusion and urban myth, so the total facts from you experts would be great.
(Possibly, it would be difficult to secure accurate online references for this - my quick searching anyway only revealed patchy, out-of-date looking stuffs. Note for example, the Wikipedia article on Cabin Pressurization has only one poor, no-referenced sentence on the whole matter!)
Note for example... Spray bottles (pressurized) in the checked luggage?