Re: A thought on regenerations (spoilers for "Night/Day of the Doctor"
After seeing the leaked plot of the Christmas special all I'm going to say is that the regeneration follows this part of Ozzy Osbourne's No More Tears.
The light in the window is a crack in the sky
A stairway to darkness in the blink of an eye
A levee of tears to learn she'll never be coming back
The man in the dark will bring another attack.
The greatest science fiction series of all time is
Doctor Who! And I'll take you all on, one-by-one
or all in a bunch to back it up!"
--- Harlan Ellison, from his introduction
to the PINNACLE series of Doctor Who books