pub fn apply(
scene: &mut Scene,
uses: &mut Uses,
patch: &Patch,
) -> Result<Applied, String>Expand description
Applies a patch to scene, whose files uses counts, or says why it
can’t — leaving both as they were. The work is the patch’s: each
operation finds its nodes by id, and the files no node uses any more are
dropped by count, never by a walk of the scene.