Sends its children to the Out. Content commits after the In, before paint.
Renders the content. Mount one per tunnel: each Out renders a copy. Mounted together with Ins, paints empty once. Suspends once on mount to check its renderer. Renders empty on the server until hydration.
Re-reads order from the fiber tree. Needed only while the commit hook is off; dev warns when it falls back.
A tunnel created by fiberTunnel.