The roottreerefchildref setting, causes entity declarations referenced anywhere in the document tree (that is, in the root document or its children) to be written in the root document's subset, and declarations for entities referenced immediately with a child to be written in the subset of each child. This produces valid SGML in that the root document contains declarations for all entities referenced in the document tree, and additionally writes all entity declarations currently referenced by a file entity in a special comment subset at the front of the file entity.

This option has all the benefits of rootallchildref and additionally purges the root document of declarations to unreferenced entities. It takes longer to save documents with this setting, so its primary value may be to periodically “clean” your documents.