Happy new year people!

With the new year I'm bumping on how perform the write of the CSD on a 
SD using SPI mode.
I'm able to put the SD in SPI and then perform read/write operations, 
setting some parameters, but I'm not able to getting work of the CMD27 
command which it write some bit in the CSD register.
Documentation I own is enough foggy, purposely foggy I say.
I guess SD Card Association keep it almost secret in order to retrieve 
adhesions at its society which it isn't for free but by pay.
I could be wrong on that, though the datasheets that I know normally 
they aren't so foggy but rather comprehensive, while the ones for SD 
they are pretty unusable, IMHO.
Anyway, is there somebody who can explain me, better if using examples, 
how the CMD27 work?
Or, does anyone know where to find detailed documentation on how to run 
commands on the SD cards?
I mean something complete maybe with some example.
I made searches everywhere on the net but I only found foggy 
documentations about the SD/MMC world.
I'd like to master SD matter one day or another, only I need your help 
and the right documentations of course.
Thanks in advance.

Victor