diff --git a/go.mod b/go.mod
index e1cd405..f11000f 100644
--- a/go.mod
+++ b/go.mod
@@ -6,7 +6,7 @@ require (
 	github.com/miekg/dns v1.1.62
 	github.com/rbmk-project/common v0.4.0
 	github.com/rbmk-project/dnscore v0.6.0
-	github.com/rbmk-project/x v0.0.0-20241129091418-83d898f771ef
+	github.com/rbmk-project/x v0.0.0-20241129115026-1ae0b6afd0db
 	github.com/spf13/pflag v1.0.5
 	github.com/stretchr/testify v1.9.0
 )
diff --git a/go.sum b/go.sum
index 05dc6a3..355364a 100644
--- a/go.sum
+++ b/go.sum
@@ -8,8 +8,8 @@ github.com/rbmk-project/common v0.4.0 h1:gw7f/YdPxcUZ81cO9IMzEPDhsc6tOUte1m0OFi6
 github.com/rbmk-project/common v0.4.0/go.mod h1:uzrFIJl8SEOpgS2pSeBFLUgqc4D1lIcGk/EYuxkFO0U=
 github.com/rbmk-project/dnscore v0.6.0 h1:23rRsLBwTkQqJQMVPf4kimzGSZsw29EY7u3ffHbWkKg=
 github.com/rbmk-project/dnscore v0.6.0/go.mod h1:Ct9RhR8HTI6tnq6/HSbzB/F8bk3k7E/6hmEctxSecUQ=
-github.com/rbmk-project/x v0.0.0-20241129091418-83d898f771ef h1:4+h9APkbuAP1d1PMQ4K279Rpe+J5XRHKf+3z85RHE9o=
-github.com/rbmk-project/x v0.0.0-20241129091418-83d898f771ef/go.mod h1:1Du1EHDkRs9D7MmpLPKAuBzZuJXRbvpBbefW0bTBVbs=
+github.com/rbmk-project/x v0.0.0-20241129115026-1ae0b6afd0db h1:5w5kA2sSKIM0fQiALZG5TbP2C0Y6PKQFWSDxkm3QHfw=
+github.com/rbmk-project/x v0.0.0-20241129115026-1ae0b6afd0db/go.mod h1:1Du1EHDkRs9D7MmpLPKAuBzZuJXRbvpBbefW0bTBVbs=
 github.com/rogpeppe/go-internal v1.13.1 h1:KvO1DLK/DRN07sQ1LQKScxyZJuNnedQ5/wKSR38lUII=
 github.com/rogpeppe/go-internal v1.13.1/go.mod h1:uMEvuHeurkdAXX61udpOXGD/AzZDWNMNyH2VO9fmH0o=
 github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
diff --git a/internal/qa/event.go b/internal/qa/event.go
index 8ccd16e..4ba5284 100644
--- a/internal/qa/event.go
+++ b/internal/qa/event.go
@@ -84,6 +84,10 @@ type Event struct {
 	// Err is the Go error that occurred.
 	Err string `json:"err,omitempty"`
 
+	// ErrClass is the error classification to a fixed set
+	// or enumerated strings or "" on success.
+	ErrClass string `json:"errClass,omitempty"`
+
 	//
 	// I/O operations
 	//
@@ -159,6 +163,7 @@ func (ev *Event) VerifyReadWriteClose(t Driver) {
 		ev.verifyEndpoint(t, ev.LocalAddr)
 		ev.verifyEndpoint(t, ev.RemoteAddr)
 		ev.verifyErrEmpty(t)
+		ev.verifyErrClassEmpty(t)
 		ev.verifyIOBufferSizePositive(t)
 		ev.verifyIOBytesCountZero(t)
 
@@ -168,6 +173,7 @@ func (ev *Event) VerifyReadWriteClose(t Driver) {
 		ev.verifyEndpoint(t, ev.LocalAddr)
 		ev.verifyEndpoint(t, ev.RemoteAddr)
 		ev.verifyErrEmpty(t)
+		ev.verifyErrClassEmpty(t)
 		ev.verifyIOBufferSizeZero(t)
 		ev.verifyIOBytesCountZero(t)
 
@@ -178,6 +184,7 @@ func (ev *Event) VerifyReadWriteClose(t Driver) {
 		ev.verifyEndpoint(t, ev.RemoteAddr)
 		ev.verifyIOBufferSizeZero(t)
 		ev.verifyIOBytesCountOrErr(t)
+		ev.verifyIOBytesCountOrErrClass(t)
 
 	case "closeDone":
 		ev.verifyDoneEventTime(t)
@@ -236,6 +243,10 @@ func (ev *Event) verifyErrEmpty(t Driver) {
 	require.Empty(t, ev.Err, "expected empty error field")
 }
 
+func (ev *Event) verifyErrClassEmpty(t Driver) {
+	require.Empty(t, ev.ErrClass, "expected empty errClass field")
+}
+
 func (ev *Event) verifyIOBufferSizePositive(t Driver) {
 	require.True(t, ev.IOBufferSize > 0, "expected positive ioBufferSize field")
 }
@@ -252,6 +263,10 @@ func (ev *Event) verifyIOBytesCountOrErr(t Driver) {
 	require.True(t, ev.IOBytesCount > 0 || ev.Err != "", "expected ioBytesCount > 0 or err != \"\"")
 }
 
+func (ev *Event) verifyIOBytesCountOrErrClass(t Driver) {
+	require.True(t, ev.IOBytesCount > 0 || ev.ErrClass != "", "expected ioBytesCount > 0 or errClass != \"\"")
+}
+
 func (ev *Event) verifyDNSRawQueryEmpty(t Driver) {
 	require.Empty(t, ev.DNSRawQuery, "expected empty dnsRawQuery field")
 }