Added a paragraph to the Usage documentation
Added a paragraph to the Usage documentation

It is about that normalization and coercision is done on a copy of the
document and not the original. Right now it is not obvious

nicolaiarocci/cerberus,funkyfuture/cerberus,dkellner/cerberus,dkellner/cerberus,funkyfuture/cerberus,nicolaiarocci/cerberus,pyeve/cerberus,pyeve/cerberus