Sentynel wrote: you don't need to know every single little detail about something to use it briefly in your story.
It would be interesting to see how much Stroud did map out. Hopefully we'll all know someday- if the Bartimaeus Bible is ever published, that is. Robert Jordan (may he rest in peace, in nomine patris, et filii, et spiritus sancti, amen), along with Teresa Patterson, published
The World of Rober Jordan's Wheel of Time and there are tons of guides to the universe of Harry Potter and the writings about Tolkien's middle earth very nearly outnumber the stars- why shouldn't something similar be published for this trilogy?
"Generally hearts are considered to be instrumental to the functions of the body, so it seems that using it as a weapon would be just as detrimental to yourself as it would be to your enemies.
Of course, perhaps it works differently for those with hearts of stone." -Dansariki