[ccp4bb] 'flatten-solvent' option in 3D auto-refine

[Eaazhisai Kandiah]

Dear Sjors,

In 3D auto-refine routine, what does the "flatten-solvent" option does? 
Specifically, i'd like to know is there a mask involved and if yes, what kind 
of mask? 

Thanks for this and for your explanations in Grenoble.

Isai