microsoft
diff --git a/src/compiler/binder.ts b/src/compiler/binder.ts
@@ -226,7 +226,7 @@ module ts {
         function bindConstructorDeclaration(node: ConstructorDeclaration) {
             bindDeclaration(node, SymbolFlags.Constructor, 0);
             forEach(node.parameters, p => {
-                if (p.flags & (NodeFlags.Public | NodeFlags.Private)) {
+                if (p.flags & (NodeFlags.Public | NodeFlags.Private | NodeFlags.Protected)) {
                     bindDeclaration(p, SymbolFlags.Property, SymbolFlags.PropertyExcludes);
                 }
             });

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
diff --git a/src/compiler/diagnosticInformationMap.generated.ts b/src/compiler/diagnosticInformationMap.generated.ts
@@ -138,9 +138,9 @@ module ts {
         Type_0_is_not_assignable_to_type_1_Colon: { code: 2322, category: DiagnosticCategory.Error, key: "Type '{0}' is not assignable to type '{1}':" },
         Type_0_is_not_assignable_to_type_1: { code: 2323, category: DiagnosticCategory.Error, key: "Type '{0}' is not assignable to type '{1}'." },
         Property_0_is_missing_in_type_1: { code: 2324, category: DiagnosticCategory.Error, key: "Property '{0}' is missing in type '{1}'." },
-        Private_property_0_cannot_be_reimplemented: { code: 2325, category: DiagnosticCategory.Error, key: "Private property '{0}' cannot be reimplemented." },
+        Property_0_is_private_in_type_1_but_not_in_type_2: { code: 2325, category: DiagnosticCategory.Error, key: "Property '{0}' is private in type '{1}' but not in type '{2}'." },
         Types_of_property_0_are_incompatible_Colon: { code: 2326, category: DiagnosticCategory.Error, key: "Types of property '{0}' are incompatible:" },
-        Required_property_0_cannot_be_reimplemented_with_optional_property_in_1: { code: 2327, category: DiagnosticCategory.Error, key: "Required property '{0}' cannot be reimplemented with optional property in '{1}'." },
+        Property_0_is_optional_in_type_1_but_required_in_type_2: { code: 2327, category: DiagnosticCategory.Error, key: "Property '{0}' is optional in type '{1}' but required in type '{2}'." },
         Types_of_parameters_0_and_1_are_incompatible_Colon: { code: 2328, category: DiagnosticCategory.Error, key: "Types of parameters '{0}' and '{1}' are incompatible:" },
         Index_signature_is_missing_in_type_0: { code: 2329, category: DiagnosticCategory.Error, key: "Index signature is missing in type '{0}'." },
         Index_signatures_are_incompatible_Colon: { code: 2330, category: DiagnosticCategory.Error, key: "Index signatures are incompatible:" },
@@ -153,8 +153,8 @@ module ts {
         Super_calls_are_not_permitted_outside_constructors_or_in_nested_functions_inside_constructors: { code: 2337, category: DiagnosticCategory.Error, key: "Super calls are not permitted outside constructors or in nested functions inside constructors" },
         super_property_access_is_permitted_only_in_a_constructor_member_function_or_member_accessor_of_a_derived_class: { code: 2338, category: DiagnosticCategory.Error, key: "'super' property access is permitted only in a constructor, member function, or member accessor of a derived class" },
         Property_0_does_not_exist_on_type_1: { code: 2339, category: DiagnosticCategory.Error, key: "Property '{0}' does not exist on type '{1}'." },
-        Only_public_methods_of_the_base_class_are_accessible_via_the_super_keyword: { code: 2340, category: DiagnosticCategory.Error, key: "Only public methods of the base class are accessible via the 'super' keyword" },
-        Property_0_is_inaccessible: { code: 2341, category: DiagnosticCategory.Error, key: "Property '{0}' is inaccessible." },
+        Only_public_and_protected_methods_of_the_base_class_are_accessible_via_the_super_keyword: { code: 2340, category: DiagnosticCategory.Error, key: "Only public and protected methods of the base class are accessible via the 'super' keyword" },
+        Property_0_is_private_and_only_accessible_within_class_1: { code: 2341, category: DiagnosticCategory.Error, key: "Property '{0}' is private and only accessible within class '{1}'." },
         An_index_expression_argument_must_be_of_type_string_number_or_any: { code: 2342, category: DiagnosticCategory.Error, key: "An index expression argument must be of type 'string', 'number', or 'any'." },
         Type_0_does_not_satisfy_the_constraint_1_Colon: { code: 2343, category: DiagnosticCategory.Error, key: "Type '{0}' does not satisfy the constraint '{1}':" },
         Type_0_does_not_satisfy_the_constraint_1: { code: 2344, category: DiagnosticCategory.Error, key: "Type '{0}' does not satisfy the constraint '{1}'." },
@@ -198,7 +198,7 @@ module ts {
         Specialized_overload_signature_is_not_assignable_to_any_non_specialized_signature: { code: 2382, category: DiagnosticCategory.Error, key: "Specialized overload signature is not assignable to any non-specialized signature." },
         Overload_signatures_must_all_be_exported_or_not_exported: { code: 2383, category: DiagnosticCategory.Error, key: "Overload signatures must all be exported or not exported." },
         Overload_signatures_must_all_be_ambient_or_non_ambient: { code: 2384, category: DiagnosticCategory.Error, key: "Overload signatures must all be ambient or non-ambient." },
-        Overload_signatures_must_all_be_public_or_private: { code: 2385, category: DiagnosticCategory.Error, key: "Overload signatures must all be public or private." },
+        Overload_signatures_must_all_be_public_private_or_protected: { code: 2385, category: DiagnosticCategory.Error, key: "Overload signatures must all be public, private or protected." },
         Overload_signatures_must_all_be_optional_or_required: { code: 2386, category: DiagnosticCategory.Error, key: "Overload signatures must all be optional or required." },
         Function_overload_must_be_static: { code: 2387, category: DiagnosticCategory.Error, key: "Function overload must be static." },
         Function_overload_must_not_be_static: { code: 2388, category: DiagnosticCategory.Error, key: "Function overload must not be static." },
@@ -255,6 +255,11 @@ module ts {
         Import_declaration_in_an_ambient_external_module_declaration_cannot_reference_external_module_through_relative_external_module_name: { code: 2439, category: DiagnosticCategory.Error, key: "Import declaration in an ambient external module declaration cannot reference external module through relative external module name." },
         Import_declaration_conflicts_with_local_declaration_of_0: { code: 2440, category: DiagnosticCategory.Error, key: "Import declaration conflicts with local declaration of '{0}'" },
         Duplicate_identifier_0_Compiler_reserves_name_1_in_top_level_scope_of_an_external_module: { code: 2441, category: DiagnosticCategory.Error, key: "Duplicate identifier '{0}'. Compiler reserves name '{1}' in top level scope of an external module." },
+        Types_have_separate_declarations_of_a_private_property_0: { code: 2442, category: DiagnosticCategory.Error, key: "Types have separate declarations of a private property '{0}'." },
+        Property_0_is_protected_but_type_1_is_not_a_class_derived_from_2: { code: 2443, category: DiagnosticCategory.Error, key: "Property '{0}' is protected but type '{1}' is not a class derived from '{2}'." },
+        Property_0_is_protected_in_type_1_but_public_in_type_2: { code: 2444, category: DiagnosticCategory.Error, key: "Property '{0}' is protected in type '{1}' but public in type '{2}'." },
+        Property_0_is_protected_and_only_accessible_within_class_1_and_its_subclasses: { code: 2445, category: DiagnosticCategory.Error, key: "Property '{0}' is protected and only accessible within class '{1}' and its subclasses." },
+        Property_0_is_protected_and_only_accessible_through_an_instance_of_class_1: { code: 2446, category: DiagnosticCategory.Error, key: "Property '{0}' is protected and only accessible through an instance of class '{1}'." },
         Import_declaration_0_is_using_private_name_1: { code: 4000, category: DiagnosticCategory.Error, key: "Import declaration '{0}' is using private name '{1}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_name_1_from_private_module_2: { code: 4001, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using name '{1}' from private module '{2}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_private_name_1: { code: 4002, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using private name '{1}'." },

diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
@@ -544,15 +544,15 @@
         "category": "Error",
         "code": 2324
     },
-    "Private property '{0}' cannot be reimplemented.": {
+    "Property '{0}' is private in type '{1}' but not in type '{2}'.": {
         "category": "Error",
         "code": 2325
     },
     "Types of property '{0}' are incompatible:": {
         "category": "Error",
         "code": 2326
     },
-    "Required property '{0}' cannot be reimplemented with optional property in '{1}'.": {
+	"Property '{0}' is optional in type '{1}' but required in type '{2}'.": {
         "category": "Error",
         "code": 2327
     },
@@ -604,11 +604,11 @@
         "category": "Error",
         "code": 2339
     },
-    "Only public methods of the base class are accessible via the 'super' keyword": {
+    "Only public and protected methods of the base class are accessible via the 'super' keyword": {
         "category": "Error",
         "code": 2340
     },
-    "Property '{0}' is inaccessible.": {
+    "Property '{0}' is private and only accessible within class '{1}'.": {
         "category": "Error",
         "code": 2341
     },
@@ -784,7 +784,7 @@
         "category": "Error",
         "code": 2384
     },
-    "Overload signatures must all be public or private.": {
+    "Overload signatures must all be public, private or protected.": {
         "category": "Error",
         "code": 2385
     },
@@ -1012,7 +1012,26 @@
         "category": "Error",
         "code": 2441
     },
-
+    "Types have separate declarations of a private property '{0}'.": {
+        "category": "Error",
+        "code": 2442
+    },
+    "Property '{0}' is protected but type '{1}' is not a class derived from '{2}'.": {
+        "category": "Error",
+        "code": 2443
+    },
+    "Property '{0}' is protected in type '{1}' but public in type '{2}'.": {
+        "category": "Error",
+        "code": 2444
+    },
+    "Property '{0}' is protected and only accessible within class '{1}' and its subclasses.": {
+        "category": "Error",
+        "code": 2445
+    },
+    "Property '{0}' is protected and only accessible through an instance of class '{1}'.": {
+        "category": "Error",
+        "code": 2446
+    },
 
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",

diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
@@ -2371,12 +2371,18 @@ module ts {
                     if (node.flags & NodeFlags.Private) {
                         write("private ");
                     }
+                    else if (node.flags & NodeFlags.Protected) {
+                        write("protected ");
+                    }
                     write("static ");
                 }
                 else {
                     if (node.flags & NodeFlags.Private) {
                         write("private ");
                     }
+                    else if (node.flags & NodeFlags.Protected) {
+                        write("protected ");
+                    }
                     // If the node is parented in the current source file we need to emit export declare or just export
                     else if (node.parent === currentSourceFile) {
                         // If the node is exported 

diff --git a/src/compiler/parser.ts b/src/compiler/parser.ts
@@ -623,6 +623,7 @@ module ts {
         switch (token) {
             case SyntaxKind.PublicKeyword:
             case SyntaxKind.PrivateKeyword:
+            case SyntaxKind.ProtectedKeyword:
             case SyntaxKind.StaticKeyword:
             case SyntaxKind.ExportKeyword:
             case SyntaxKind.DeclareKeyword:
@@ -2920,6 +2921,7 @@ module ts {
                     }
                 case SyntaxKind.PublicKeyword:
                 case SyntaxKind.PrivateKeyword:
+                case SyntaxKind.ProtectedKeyword:
                 case SyntaxKind.StaticKeyword:
                     // When followed by an identifier or keyword, these do not start a statement but
                     // might instead be following type members
@@ -3238,6 +3240,8 @@ module ts {
             var lastDeclareModifierLength: number;
             var lastPrivateModifierStart: number;
             var lastPrivateModifierLength: number;
+            var lastProtectedModifierStart: number;
+            var lastProtectedModifierLength: number;
 
             while (true) {
                 var modifierStart = scanner.getTokenPos();
@@ -3277,6 +3281,21 @@ module ts {
                         flags |= NodeFlags.Private;
                         break;
 
+                    case SyntaxKind.ProtectedKeyword:
+                        if (flags & NodeFlags.Public || flags & NodeFlags.Private || flags & NodeFlags.Protected) {
+                            grammarErrorAtPos(modifierStart, modifierLength, Diagnostics.Accessibility_modifier_already_seen);
+                        }
+                        else if (flags & NodeFlags.Static) {
+                            grammarErrorAtPos(modifierStart, modifierLength, Diagnostics._0_modifier_must_precede_1_modifier, "protected", "static");
+                        }
+                        else if (context === ModifierContext.ModuleElements || context === ModifierContext.SourceElements) {
+                            grammarErrorAtPos(modifierStart, modifierLength, Diagnostics._0_modifier_cannot_appear_on_a_module_element, "protected");
+                        }
+                        lastProtectedModifierStart = modifierStart;
+                        lastProtectedModifierLength = modifierLength;
+                        flags |= NodeFlags.Protected;
+                        break;
+
                     case SyntaxKind.StaticKeyword:
                         if (flags & NodeFlags.Static) {
                             grammarErrorAtPos(modifierStart, modifierLength, Diagnostics._0_modifier_already_seen, "static");
@@ -3334,6 +3353,9 @@ module ts {
             else if (token === SyntaxKind.ConstructorKeyword && flags & NodeFlags.Private) {
                 grammarErrorAtPos(lastPrivateModifierStart, lastPrivateModifierLength, Diagnostics._0_modifier_cannot_appear_on_a_constructor_declaration, "private");
             }
+            else if (token === SyntaxKind.ConstructorKeyword && flags & NodeFlags.Protected) {
+                grammarErrorAtPos(lastProtectedModifierStart, lastProtectedModifierLength, Diagnostics._0_modifier_cannot_appear_on_a_constructor_declaration, "protected");
+            }
             else if (token === SyntaxKind.ImportKeyword) {
                 if (flags & NodeFlags.Ambient) {
                     grammarErrorAtPos(lastDeclareModifierStart, lastDeclareModifierLength, Diagnostics.A_declare_modifier_cannot_be_used_with_an_import_declaration, "declare");
@@ -3610,6 +3632,7 @@ module ts {
                 case SyntaxKind.DeclareKeyword:
                 case SyntaxKind.PublicKeyword:
                 case SyntaxKind.PrivateKeyword:
+                case SyntaxKind.ProtectedKeyword:
                 case SyntaxKind.StaticKeyword:
                     // Check for modifier on source element
                     return lookAhead(() => { nextToken(); return isDeclaration(); });

diff --git a/src/compiler/types.ts b/src/compiler/types.ts
@@ -234,13 +234,14 @@ module ts {
         Rest             = 0x00000008,  // Parameter
         Public           = 0x00000010,  // Property/Method
         Private          = 0x00000020,  // Property/Method
-        Static           = 0x00000040,  // Property/Method
-        MultiLine        = 0x00000080,  // Multi-line array or object literal
-        Synthetic        = 0x00000100,  // Synthetic node (for full fidelity)
-        DeclarationFile  = 0x00000200,  // Node is a .d.ts file
-
-        Modifier = Export | Ambient | Public | Private | Static,
-        AccessibilityModifier = Public | Private
+        Protected        = 0x00000040,  // Property/Method
+        Static           = 0x00000080,  // Property/Method
+        MultiLine        = 0x00000100,  // Multi-line array or object literal
+        Synthetic        = 0x00000200,  // Synthetic node (for full fidelity)
+        DeclarationFile  = 0x00000400,  // Node is a .d.ts file
+
+        Modifier = Export | Ambient | Public | Private | Protected | Static,
+        AccessibilityModifier = Public | Private | Protected
     }
 
     export interface Node extends TextRange {

diff --git a/...assAndModuleThatMergeWithModulesExportedStaticFunctionUsingClassPrivateStatics.errors.txt b/...assAndModuleThatMergeWithModulesExportedStaticFunctionUsingClassPrivateStatics.errors.txt
@@ -1,4 +1,4 @@
-tests/cases/conformance/internalModules/DeclarationMerging/ClassAndModuleThatMergeWithModulesExportedStaticFunctionUsingClassPrivateStatics.ts(11,16): error TS2341: Property 'clodule.sfn' is inaccessible.
+tests/cases/conformance/internalModules/DeclarationMerging/ClassAndModuleThatMergeWithModulesExportedStaticFunctionUsingClassPrivateStatics.ts(11,16): error TS2341: Property 'sfn' is private and only accessible within class 'clodule<T>'.
 
 
 ==== tests/cases/conformance/internalModules/DeclarationMerging/ClassAndModuleThatMergeWithModulesExportedStaticFunctionUsingClassPrivateStatics.ts (1 errors) ====
@@ -14,7 +14,7 @@ tests/cases/conformance/internalModules/DeclarationMerging/ClassAndModuleThatMer
         export function fn<T>(x: T, y: T): number {
             return clodule.sfn('a');
                    ~~~~~~~~~~~
-!!! error TS2341: Property 'clodule.sfn' is inaccessible.
+!!! error TS2341: Property 'sfn' is private and only accessible within class 'clodule<T>'.
         }
     }