+ /**
+ * \brief AVOID using the following fourth field at all costs.
+ *
+ * They are at least two good reasons for NOT using fourth:
+ * - the main reason is that it is NOT part of the 'official'
+ * Dicom Dictionnary.
+ * - a second reason is that it is not defined for all the groups.
+ * .
+ * Still it provides some semantics as group name abbreviation that
+ * can prove of some help when organizing things in an interface.
+ * For the time being we keep it in gdcm but it migth be removed in
+ * future releases it proves to be source of confusion.
+ * Here is a small dictionary we encountered in "nature":
+ * - CMD Command
+ * - META Meta Information
+ * - DIR Directory
+ * - ID ???
+ * - PAT Patient
+ * - ACQ Acquisition
+ * - REL Related
+ * - IMG Image
+ * - SDY Study
+ * - VIS Visit
+ * - WAV Waveform
+ * - PRC ???
+ * - DEV Device
+ * - NMI Nuclear Medicine
+ * - MED ???
+ * - BFS Basic Film Session
+ * - BFB Basic Film Box
+ * - BIB Basic Image Box
+ * - BAB
+ * - IOB
+ * - PJ
+ * - PRINTER
+ * - RT Radio Therapy
+ * - DVH
+ * - SSET
+ * - RES Results
+ * - CRV Curve
+ * - OLY Overlays
+ * - PXL Pixels
+ * - DL Delimiters
+ * .
+ *
+ * Other usefull abreviations used for Radiographic view associated with
+ * Patient Position (0018,5100):
+ * - AP = Anterior/Posterior
+ * - PA = Posterior/Anterior
+ * - LL = Left Lateral
+ * - RL = Right Lateral
+ * - RLD = Right Lateral Decubitus
+ * - LLD = Left Lateral Decubitus
+ * - RLO = Right Lateral Oblique
+ * - LLO = Left Lateral Oblique
+ * .
+ */
+ TagName Fourth;
+
+ /// e.g. "Patient's Name"
+ TagName Name;
+
+ /// Redundant with (group, element) but we add it for efficiency purpose.
+ TagKey Key;
+};
+} // end namespace gdcm