Document mHoldSync and mHoldReport

src/app/ReadHandler.h

@@ -217,6 +217,8 @@ class ReadHandler : public Messaging::ExchangeDelegate
     uint16_t mMinIntervalFloorSeconds   = 0;
     uint16_t mMaxIntervalCeilingSeconds = 0;
     SessionHolder mSessionHandle;
+    // only for subscription, mHoldReport is set to true on report delivery within min interval, and then allow to send report after
+    // min interval. if there is urgent event delivery, mHoldReport is also set as false.
     bool mHoldReport         = false;
     bool mDirty              = false;
     bool mActiveSubscription = false;
@@ -226,8 +228,9 @@ class ReadHandler : public Messaging::ExchangeDelegate
     NodeId mInitiatorNodeId                                  = kUndefinedNodeId;
     AttributePathExpandIterator mAttributePathExpandIterator = AttributePathExpandIterator(nullptr);
     bool mIsFabricFiltered                                   = false;
-    bool mHoldSync                                           = false;
-    uint32_t mLastWrittenEventsBytes                         = 0;
+    // only for subscription, mHoldSync means empty sync report can be generated after max interval,
+    bool mHoldSync                   = false;
+    uint32_t mLastWrittenEventsBytes = 0;
     SubjectDescriptor mSubjectDescriptor;
     // The detailed encoding state for a single attribute, used by list chunking feature.
     AttributeValueEncoder::AttributeEncodeState mAttributeEncoderState;