When I am honest I must say that the documentation on Wiki is good, but it mostly scratches the surface for stm32, it is more in-depth for AVR
In fairness, there's been a lot of people working on understanding the AVR family largely because of the Arduino's popularity. They've been helped by the fact that there's a lot of commonality in control registers and peripherals across the range, and that not having an OS most AVR boards make it pretty obvious when something's not quite right (none of this "is the hardware not doing what I want or have I got the API parameters wrong?").
While ARM chips have been round for decades and have been fairly accessible since the days of the NSLU2 "Slug" and various "smart plugs" etc., the STM32 with its particular mix of control registers is much more recent and has attracted /relatively/ little attention.
In both cases I miss the simplicity of being able to attach a logic analyser onto the system bus, but that's another issue entirely.
MarkMLl