diff --git a/moo/README.md b/moo/README.md
index 75b2e0f..d5b0fb4 100644
--- a/moo/README.md
+++ b/moo/README.md
@@ -81,3 +81,14 @@ while (true)
 1 to: 20 do: [:count | ... ].
 ~~~
 
+
+### Exception handling
+Exception signal.
+Exception signal: "message".
+
+[ ... ] on: Exception do: [:ex | ... ].
+
+ex retry.
+ex resume.
+ex resume: value.
+ex return: value.
diff --git a/moo/kernel/Apex.moo b/moo/kernel/Apex.moo
index cff1240..10146f8 100644
--- a/moo/kernel/Apex.moo
+++ b/moo/kernel/Apex.moo
@@ -313,8 +313,6 @@ class UndefinedObject(Apex)
 	}
 }
 
-
-
 extend Error
 {
 	/* ----------------------------
@@ -343,6 +341,7 @@ extend Error
 
 	method(#primitive) asString.
 
+/* -----------------------
 	method signal
 	{
 		| exctx exblk retval actpos ctx |
@@ -367,17 +366,8 @@ extend Error
 		// -----------------------------------------------------------------
 		//thisContext unwindTo: nil return: nil.
 		//thisContext unwindTo: (Processor activeProcess initialContext) return: nil.
-		
-// TOOD: IMPROVE THIS EXPERIMENTAL BACKTRACE...
-System logNl: "== BACKTRACE ==".
-ctx := thisContext.
-while (ctx notNil)
-{
-	if (ctx class == MethodContext) { System logNl: (" " & ctx method owner name & ">>" & ctx method name) }.
-	// TODO: include blockcontext???
-	ctx := ctx sender.
-}.
-System logNl: "== END OF BACKTRACE ==".
+
+		System backtrace.
 
 		thisContext unwindTo: (thisProcess initialContext) return: nil.
 		("### ERROR NOT HANDLED #### " & self class name & " - " & self asString) dump.
@@ -386,4 +376,5 @@ System logNl: "== END OF BACKTRACE ==".
 		//Processor activeProcess terminate.
 		thisProcess terminate.
 	}
+---------------------- */
 }
diff --git a/moo/kernel/Except.moo b/moo/kernel/Except.moo
index a20fa52..bc1f2b2 100644
--- a/moo/kernel/Except.moo
+++ b/moo/kernel/Except.moo
@@ -69,21 +69,7 @@ TODO: can i convert 'thisProcess primError' to a relevant exception?
 		//thisContext unwindTo: nil return: nil.
 		//thisContext unwindTo: (Processor activeProcess initialContext) return: nil.
 
-// TOOD: IMPROVE THIS EXPERIMENTAL BACKTRACE... MOVE THIS TO  System>>backtrace and skip the first method context for backtrace itself.
-System logNl: "== BACKTRACE ==".
-ctx := thisContext.
-while (ctx notNil)
-{
-	if (ctx class == MethodContext) 
-	{
-		System logNl: (" " & ctx method owner name & ">>" & ctx method name &
-		               " (" & ctx method sourceFile & " " & (ctx method ipSourceLine: (ctx pc)) asString & ")"). 
-// TODO: get location of the current pc and include it... (ctx method sourceLine: ctx pc) asString dump.
-	}.
-	// TODO: include blockcontext???
-	ctx := ctx sender.
-}.
-System logNl: "== END OF BACKTRACE ==".
+		System backtrace.
 
 		thisContext unwindTo: (thisProcess initialContext) return: nil.
 		("### EXCEPTION NOT HANDLED(Exception) #### " & self class name & " - " & self messageText) dump.
@@ -540,17 +526,7 @@ extend Apex
 		| class_name ctx |
 		class_name := if (self class == Class) { self name } else { self class name }.
 
-// TOOD: IMPROVE THIS EXPERIMENTAL BACKTRACE...
-System logNl: "== BACKTRACE ==".
-ctx := thisContext.
-while (ctx notNil)
-{
-	if (ctx class == MethodContext) { System logNl: (" " & ctx method owner name & ">>" & ctx method name) }.
-	// TODO: include blockcontext???
-	ctx := ctx sender.
-}.
-System logNl: "== END OF BACKTRACE ==".
-
+		System backtrace.
 
 		NoSuchMessageException signal: (message_name & " not understood by " & class_name).
 	}
diff --git a/moo/kernel/System.moo b/moo/kernel/System.moo
index 74d2890..23825e3 100644
--- a/moo/kernel/System.moo
+++ b/moo/kernel/System.moo
@@ -214,6 +214,28 @@ TODO: how to pass all variadic arguments to another variadic methods???
 		^self atLevel: System.Log.INFO logNl: message and: message2.
 	}
 
+	method(#class) backtrace
+	{
+		| ctx |
+		// TOOD: IMPROVE THIS EXPERIMENTAL BACKTRACE... MOVE THIS TO  System>>backtrace and skip the first method context for backtrace itself.
+		System logNl: "== BACKTRACE ==".
+
+		//ctx := thisContext.
+		ctx := thisContext sender. // skip the current context. skip to the caller context.
+		while (ctx notNil)
+		{
+			if (ctx class == MethodContext) 
+			{
+				System logNl: (" " & ctx method owner name & ">>" & ctx method name &
+							   " (" & ctx method sourceFile & " " & (ctx method ipSourceLine: (ctx pc)) asString & ")"). 
+		// TODO: get location of the current pc and include it... (ctx method sourceLine: ctx pc) asString dump.
+			}.
+			// TODO: include blockcontext???
+			ctx := ctx sender.
+		}.
+		System logNl: "== END OF BACKTRACE ==".
+	}
+
 	/* nsdic access */
 	method(#class) at: key
 	{
diff --git a/moo/kernel/test-003.moo b/moo/kernel/test-003.moo
index affb216..22dd24b 100644
--- a/moo/kernel/test-003.moo
+++ b/moo/kernel/test-003.moo
@@ -92,7 +92,8 @@ class MyObject(Object)
 			tb := tc at: idx.
 			System log(System.Log.INFO, idx asString, (if (tb value) { " PASS" } else { " FAIL" }), "\n").
 		].
-Exception signal: 'xxx'.
+
+Exception signal: 'experiment with exception signalling'.
 
 		// TODO: 
 		String format("%s", " 나	는\\\"") dump.
diff --git a/moo/lib/debug.c b/moo/lib/debug.c
index 021af28..1423e0a 100644
--- a/moo/lib/debug.c
+++ b/moo/lib/debug.c
@@ -241,9 +241,9 @@ int moo_addmethodtodbgi (moo_t* moo, moo_oow_t file_offset, moo_oow_t class_offs
 	di->_file = file_offset;
 	di->_class = class_offset;
 	di->start_line = start_line;
-	di->code_loc_start = name_bytes_aligned;
+	di->code_loc_start = name_bytes_aligned; /* distance from the beginning of the variable payload */
 	di->code_loc_len = code_loc_len;
-	di->text_start = name_bytes_aligned + code_loc_bytes_aligned;
+	di->text_start = name_bytes_aligned + code_loc_bytes_aligned; /* distance from the beginning of the variable payload */
 	di->text_len = text_len;
 
 	curptr = (moo_uint8_t*)(di + 1);
diff --git a/moo/lib/exec.c b/moo/lib/exec.c
index 20f2742..8fe95ff 100644
--- a/moo/lib/exec.c
+++ b/moo/lib/exec.c
@@ -2228,7 +2228,7 @@ static MOO_INLINE moo_dbgi_method_t* get_dbgi_method (moo_t* moo, moo_oop_method
 		if (dbgi_method_offset > 0)
 		{
 			MOO_ASSERT (moo, dbgi_method_offset < moo->dbgi->_len);
-			di = (moo_dbgi_method_t*)&((moo_uint8_t*)moo->dbgi)[dbgi_method_offset];
+			di = (moo_dbgi_method_t*)MOO_DBGI_GET_DATA(moo, dbgi_method_offset);
 			MOO_ASSERT (moo, MOO_DBGI_GET_TYPE_CODE(di->_type) == MOO_DBGI_TYPE_CODE_METHOD);
 		}
 	}
@@ -2258,7 +2258,7 @@ static moo_pfrc_t pf_method_get_source_file (moo_t* moo, moo_mod_t* mod, moo_ooi
 				const moo_ooch_t* file_name;
 
 				MOO_ASSERT (moo, dbgi_file_offset < moo->dbgi->_len);
-				di = (moo_dbgi_file_t*)&((moo_uint8_t*)moo->dbgi)[dbgi_file_offset];
+				di = (moo_dbgi_file_t*)MOO_DBGI_GET_DATA(moo, dbgi_file_offset);
 				MOO_ASSERT (moo, MOO_DBGI_GET_TYPE_CODE(di->_type) == MOO_DBGI_TYPE_CODE_FILE);
 
 				file_name = (const moo_ooch_t*)(di + 1);
@@ -2300,7 +2300,6 @@ static moo_pfrc_t pf_method_get_ip_source_line (moo_t* moo, moo_mod_t* mod, moo_
 			retv = moo_oowtoint(moo, code_loc_ptr[ipv]);
 			if (!retv) return MOO_PF_FAILURE;
 		}
-/* TODO: security check for data corruption? check if the ipv offset and the size calcualted doesn't exceed di->_len... */
 	}
 
 	MOO_STACK_SETRET (moo, nargs, retv);
diff --git a/moo/lib/moo.h b/moo/lib/moo.h
index a1693f2..2552ada 100644
--- a/moo/lib/moo.h
+++ b/moo/lib/moo.h
@@ -973,6 +973,8 @@ typedef enum moo_dbgi_type_t moo_dbgi_type_t;
 #define MOO_DBGI_GET_TYPE_CODE(type) ((type) >> 8)
 #define MOO_DBGI_GET_TYPE_FLAGS(type) ((type) & 0xFF)
 
+#define MOO_DBGI_GET_DATA(moo, offset) ((moo_uint8_t*)(moo)->dbgi + (offset))
+
 typedef struct moo_dbgi_file_t moo_dbgi_file_t;
 struct moo_dbgi_file_t
 {