Update C++ docstrings for extended histentry

nestkernel/histentry.h

@@ -40,20 +40,22 @@ class histentry
   double t_;              //!< point in time when spike occurred (in ms)
   double Kminus_;         //!< value of Kminus at that time
   double Kminus_triplet_; //!< value of triplet STDP Kminus at that time
-  size_t access_counter_; //!< access counter to enable removal of the entry, once all neurons read it
+  size_t access_counter_; //! how often this entry was accessed (to enable removal, once read by all synapses which need it)
 };
 
-// entry in the history of plasticity rules which consider additional factors
+/**
+ * Class to represent a single entry in the spiking history of the ClopathArchivingNode or the UrbanczikArchivingNode.
+ *
+ * These history entries typically represent continuously-evolving values in time, so history timestamps correspond to ``nest.biological_time`` in simulation resolution rather than times of spikes.
+ */
 class histentry_extended
 {
 public:
   histentry_extended( double t, double dw, size_t access_counter );
 
-  double t_; //!< point in time when spike occurred (in ms)
+  double t_; //!< point in time for the history entry spike occurred (in ms)
   double dw_;
-  //! how often this entry was accessed (to enable removal, once read by all
-  //! neurons which need it)
-  size_t access_counter_;
+  size_t access_counter_;  //! how often this entry was accessed (to enable removal, once read by all synapses which need it)
 
   friend bool operator<( const histentry_extended he, double t );
 };