diff --git a/source/toy_attributes.c b/source/toy_attributes.c
index 42c10ab..c999af5 100644
--- a/source/toy_attributes.c
+++ b/source/toy_attributes.c
@@ -6,9 +6,12 @@
 #include <string.h>
 #include <ctype.h>
 
+//if set, used for delegating to user-defined code
+static Toy_OpaqueAttributeHandler opaqueAttributeCallback = NULL;
+
 //NOTE: there is no need to call 'Toy_freeValue' on the arguments, as the VM assumes you don't
 
-Toy_Value handleStringAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute) {
+Toy_Value Toy_private_handleStringAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute) {
 	if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "length", 6)  == 0) {
 		return TOY_VALUE_FROM_INTEGER(TOY_VALUE_AS_STRING(compound)->info.length);
 	}
@@ -144,7 +147,7 @@ static void attr_arraySort(Toy_VM* vm) {
 	//URGENT: attr_arraySort
 }
 
-Toy_Value handleArrayAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute) {
+Toy_Value Toy_private_handleArrayAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute) {
 	if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "length", 6)  == 0) {
 		return TOY_VALUE_FROM_INTEGER(TOY_VALUE_AS_ARRAY(compound)->count);
 	}
@@ -220,23 +223,23 @@ static void attr_tableForEach(Toy_VM* vm) {
 	//URGENT: attr_tableForEach
 }
 
-Toy_Value handleTableAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute) {
+Toy_Value Toy_private_handleTableAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute) {
 	if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "length", 6)  == 0) {
 		return TOY_VALUE_FROM_INTEGER(TOY_VALUE_AS_ARRAY(compound)->count);
 	}
-	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "insert", 4)  == 0) {
+	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "insert", 6)  == 0) {
 		Toy_Function* fn = Toy_createFunctionFromCallback(&vm->memoryBucket, attr_tableInsert);
 		return TOY_VALUE_FROM_FUNCTION(fn);
 	}
-	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "hasKey", 4)  == 0) {
+	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "hasKey", 6)  == 0) {
 		Toy_Function* fn = Toy_createFunctionFromCallback(&vm->memoryBucket, attr_tableHasKey);
 		return TOY_VALUE_FROM_FUNCTION(fn);
 	}
-	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "remove", 4)  == 0) {
+	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "remove", 6)  == 0) {
 		Toy_Function* fn = Toy_createFunctionFromCallback(&vm->memoryBucket, attr_tableRemove);
 		return TOY_VALUE_FROM_FUNCTION(fn);
 	}
-	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "forEach", 4)  == 0) {
+	else if (strncmp(TOY_VALUE_AS_STRING(attribute)->leaf.data, "forEach", 7)  == 0) { //BUG: compare the contents AND length of these strings
 		Toy_Function* fn = Toy_createFunctionFromCallback(&vm->memoryBucket, attr_tableForEach);
 		return TOY_VALUE_FROM_FUNCTION(fn);
 	}
@@ -246,4 +249,19 @@ Toy_Value handleTableAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attrib
 		Toy_error(buffer);
 		return TOY_VALUE_FROM_NULL();
 	}
+}
+
+Toy_Value Toy_private_handleOpaqueAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute) {
+	if (opaqueAttributeCallback == NULL) {
+		char buffer[256];
+		snprintf(buffer, 256, "Unknown attribute '%s' of type '%s' (did you set the opaque callbacks?)", TOY_VALUE_AS_STRING(attribute)->leaf.data, Toy_private_getValueTypeAsCString(compound.type));
+		Toy_error(buffer);
+		return TOY_VALUE_FROM_NULL();
+	}
+
+	return opaqueAttributeCallback(vm, compound, attribute);
+}
+
+void Toy_private_setOpaqueAttributeHandler(Toy_OpaqueAttributeHandler cb) {
+	opaqueAttributeCallback = cb;
 }
\ No newline at end of file
diff --git a/source/toy_attributes.h b/source/toy_attributes.h
index 29502a3..f42a8a0 100644
--- a/source/toy_attributes.h
+++ b/source/toy_attributes.h
@@ -1,12 +1,10 @@
 #pragma once
 
+#include "toy_common.h"
+
 #include "toy_value.h"
 #include "toy_vm.h"
 
-Toy_Value handleStringAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
-Toy_Value handleArrayAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
-Toy_Value handleTableAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
-
 // [x] string.length
 // [x] string.asUpper
 // [x] string.asLower
@@ -20,3 +18,12 @@ Toy_Value handleTableAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attrib
 // [x] table.hasKey(x)
 // [x] table.remove(x)
 // [ ] table.forEach(fn) // fn(x,y) -> void
+
+TOY_API Toy_Value Toy_private_handleStringAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
+TOY_API Toy_Value Toy_private_handleArrayAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
+TOY_API Toy_Value Toy_private_handleTableAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
+TOY_API Toy_Value Toy_private_handleOpaqueAttributes(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
+
+//plug-and-play attributes for custom objects
+typedef Toy_Value (*Toy_OpaqueAttributeHandler)(Toy_VM* vm, Toy_Value compound, Toy_Value attribute);
+TOY_API void Toy_private_setOpaqueAttributeHandler(Toy_OpaqueAttributeHandler cb);
diff --git a/source/toy_value.c b/source/toy_value.c
index d58bedc..37cb426 100644
--- a/source/toy_value.c
+++ b/source/toy_value.c
@@ -141,6 +141,9 @@ Toy_Value Toy_copyValue(Toy_Bucket** bucketHandle, Toy_Value value) {
 			return TOY_VALUE_FROM_FUNCTION(Toy_copyFunction(bucketHandle, value.as.function));
 
 		case TOY_VALUE_OPAQUE:
+			//copy opaques by value
+			return value;
+
 		case TOY_VALUE_ANY:
 		case TOY_VALUE_REFERENCE:
 		case TOY_VALUE_UNKNOWN:
@@ -650,7 +653,7 @@ Toy_String* Toy_stringifyValue(Toy_Bucket** bucketHandle, Toy_Value value) {
 
 		case TOY_VALUE_OPAQUE:
 			//dummy
-			return Toy_createStringLength(bucketHandle, "<opaque>", 6);
+			return Toy_createStringLength(bucketHandle, "<opaque>", 8);
 
 		case TOY_VALUE_ANY:
 		case TOY_VALUE_REFERENCE:
diff --git a/source/toy_vm.c b/source/toy_vm.c
index e0fcfdd..e765f85 100644
--- a/source/toy_vm.c
+++ b/source/toy_vm.c
@@ -428,13 +428,16 @@ static void processAttribute(Toy_VM* vm) {
 
 	//type-based attributes
 	if (TOY_VALUE_IS_STRING(compound)) {
-		result = handleStringAttributes(vm, compound, attribute);
+		result = Toy_private_handleStringAttributes(vm, compound, attribute);
 	}
 	else if (TOY_VALUE_IS_ARRAY(compound)) {
-		result = handleArrayAttributes(vm, compound, attribute);
+		result = Toy_private_handleArrayAttributes(vm, compound, attribute);
 	}
 	else if (TOY_VALUE_IS_TABLE(compound)) {
-		result = handleTableAttributes(vm, compound, attribute);
+		result = Toy_private_handleTableAttributes(vm, compound, attribute);
+	}
+	else if (TOY_VALUE_IS_OPAQUE(compound)) {
+		result = Toy_private_handleOpaqueAttributes(vm, compound, attribute);
 	}
 	else {
 		char buffer[256];