The roottreerefchildnone setting, causes entity declarations referenced anywhere in the document tree (that is, in the root doc or its children) to be written in the root document's subset, and no entity declarations to be written in childrens' subsets. This produces valid SGML in that the root document contains declarations for all entities referenced in the document tree.

This option has all the benefits/considerations of rootallchildnone 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.