fromJSON() attached child nodes through the container constructor, which
runs them back through append()/normalize(). For root-level children that
re-applies insertion spacing normalization and overwrites each node's own
raws.before with the previous sibling's, so toJSON() -> fromJSON() was not
lossless: stylesheets with non-uniform blank lines between top-level rules
came back with their spacing flattened.
Rehydrate children separately and attach them directly, keeping the raws
exactly as serialized.
Andrey Sitnik