Placeholders

Placeholders carry reuse through a conversion that would otherwise flatten it.

DITA-OT resolves conrefs and keys when it converts, so the Markdown it writes contains copies, not references. Before conversion, MANIFEST swaps each reference for a token such as @@K12@@, and records it in the reuse ledger. A token that goes missing or appears twice fails the convert step, so reuse can't be lost silently.