+/**
+ * \ref DocEntrySet is an abstract base class for \ref ElementSet
+ * and \ref SQItem which are both containers for DocEntries.
+ * \ref ElementSet is based on the STL map<> container
+ * (see \ref ElementSet::TagHT), as opposed to \ref SQItem
+ * which is based on an STL list container (see \ref SQItem::docEntries).
+ * Since the syntax for adding a new element to a map<> or a list<>
+ * differ, \ref DocEntrySet is designed as an adapter to unify the
+ * interfaces of \ref DocEntrySet and \ref ElementSet.
+ * As an illustration of this design, please refer to the implementation
+ * of \ref AddEntry (or any pure virtual method) in both derived classes.
+ * This adapter unification of interfaces enables the parsing of a
+ * DICOM header containing (optionaly heavily nested) sequences to be
+ * written recursively [see \ref Document::ParseDES
+ * which calls \ref Document::ParseSQ, which in turns calls
+ * \ref Document::ParseDES ].
+ *
+ * \note Developpers should strongly resist to the temptation of adding
+ * members to this class since this class is designed as an adapter
+ * in the form of an abstract base class.
+ */
+class GDCM_EXPORT DocEntrySet