The functions listed here no longer work.
dtdElement(name, dtd)
dtdElementValidEntry(element, name, pos=NULL)
dtdEntity(name, dtd)
dtdIsAttribute(name, element, dtd)
dtdValidElement(name, within, dtd, pos=NULL)
parseDTD(extId, asText = FALSE, name = "", isURL = FALSE, error = xmlErrorCumulator())
xmlContainsElement(name, dtd)
xmlContainsEntity(name, dtd)These functions relied on direct member access to DTD-related
structures in libxml2, which is no longer supported.