diff --git a/fluent/src/context.js b/fluent/src/context.js
index 4f96f27e0..bfe281771 100644
--- a/fluent/src/context.js
+++ b/fluent/src/context.js
@@ -50,19 +50,20 @@ export class MessageContext {
   constructor(locales, { functions = {}, useIsolating = true } = {}) {
     this.locales = Array.isArray(locales) ? locales : [locales];
 
-    this._messages = new Map();
+    this._privateMessages = new Map();
+    this._publicMessages = new Map();
     this._functions = functions;
     this._useIsolating = useIsolating;
     this._intls = new WeakMap();
   }
 
   /*
-   * Return an iterator over `[id, message]` pairs.
+   * Return an iterator over public `[id, message]` pairs.
    *
    * @returns {Iterator}
    */
   get messages() {
-    return this._messages[Symbol.iterator]();
+    return this._publicMessages[Symbol.iterator]();
   }
 
   /*
@@ -72,7 +73,7 @@ export class MessageContext {
    * @returns {bool}
    */
   hasMessage(id) {
-    return this._messages.has(id);
+    return this._publicMessages.has(id);
   }
 
   /*
@@ -85,7 +86,7 @@ export class MessageContext {
    * @returns {Any}
    */
   getMessage(id) {
-    return this._messages.get(id);
+    return this._publicMessages.get(id);
   }
 
   /**
@@ -109,7 +110,13 @@ export class MessageContext {
   addMessages(source) {
     const [entries, errors] = parse(source);
     for (const id in entries) {
-      this._messages.set(id, entries[id]);
+      if (id.startsWith('-')) {
+        // Identifiers starting with a dash (-) are considered private and
+        // cannot be retrieved from MessageContext.
+        this._privateMessages.set(id, entries[id]);
+      } else {
+        this._publicMessages.set(id, entries[id]);
+      }
     }
 
     return errors;
diff --git a/fluent/src/parser.js b/fluent/src/parser.js
index 334aa8929..e6387ce93 100644
--- a/fluent/src/parser.js
+++ b/fluent/src/parser.js
@@ -2,7 +2,9 @@
 
 const MAX_PLACEABLES = 100;
 
-const identifierRe = new RegExp('[a-zA-Z_][a-zA-Z0-9_-]*', 'y');
+const privateIdentifierRe = new RegExp('-?[a-zA-Z][a-zA-Z0-9_-]*', 'y');
+const publicIdentifierRe = new RegExp('[a-zA-Z][a-zA-Z0-9_-]*', 'y');
+const functionIdentifierRe = /^[A-Z][A-Z_?-]*$/;
 
 /**
  * The `Parser` class is responsible for parsing FTL resources.
@@ -118,7 +120,7 @@ class RuntimeParser {
    * @private
    */
   getMessage() {
-    const id = this.getIdentifier();
+    const id = this.getPrivateIdentifier();
     let attrs = null;
 
     this.skipInlineWS();
@@ -224,25 +226,44 @@ class RuntimeParser {
   }
 
   /**
-   * Get Message identifier.
+   * Get identifier of a Message, Attribute or External Attribute.
    *
    * @returns {String}
    * @private
    */
-  getIdentifier() {
-    identifierRe.lastIndex = this._index;
-
-    const result = identifierRe.exec(this._source);
+  getIdentifier(re) {
+    re.lastIndex = this._index;
+    const result = re.exec(this._source);
 
     if (result === null) {
       this._index += 1;
-      throw this.error('Expected an identifier (starting with [a-zA-Z_])');
+      throw this.error(`Expected an identifier [${re.toString()}]`);
     }
 
-    this._index = identifierRe.lastIndex;
+    this._index = re.lastIndex;
     return result[0];
   }
 
+  /**
+   * Get a potentially private identifier (staring with a dash).
+   *
+   * @returns {String}
+   * @private
+   */
+  getPrivateIdentifier() {
+    return this.getIdentifier(privateIdentifierRe);
+  }
+
+  /**
+   * Get a public identifier.
+   *
+   * @returns {String}
+   * @private
+   */
+  getPublicIdentifier() {
+    return this.getIdentifier(publicIdentifierRe);
+  }
+
   /**
    * Get Variant name.
    *
@@ -479,6 +500,12 @@ class RuntimeParser {
     const ch = this._source[this._index];
 
     if (ch === '}') {
+      if (selector.type === 'attr' && selector.id.name.startsWith('-')) {
+        throw this.error(
+          'Attributes of private messages cannot be interpolated.'
+        );
+      }
+
       return selector;
     }
 
@@ -486,6 +513,21 @@ class RuntimeParser {
       throw this.error('Expected "}" or "->"');
     }
 
+    if (selector.type === 'ref') {
+      throw this.error('Message references cannot be used as selectors.');
+    }
+
+    if (selector.type === 'var') {
+      throw this.error('Variants cannot be used as selectors.');
+    }
+
+    if (selector.type === 'attr' && !selector.id.name.startsWith('-')) {
+      throw this.error(
+        'Attributes of public messages cannot be used as selectors.'
+      );
+    }
+
+
     this._index += 2; // ->
 
     this.skipInlineWS();
@@ -526,7 +568,7 @@ class RuntimeParser {
     if (this._source[this._index] === '.') {
       this._index++;
 
-      const name = this.getIdentifier();
+      const name = this.getPublicIdentifier();
       this._index++;
       return {
         type: 'attr',
@@ -551,6 +593,10 @@ class RuntimeParser {
       this._index++;
       const args = this.getCallArgs();
 
+      if (!functionIdentifierRe.test(literal.name)) {
+        throw this.error('Function names must be all upper-case');
+      }
+
       this._index++;
 
       literal.type = 'fun';
@@ -705,7 +751,7 @@ class RuntimeParser {
       }
       this._index++;
 
-      const key = this.getIdentifier();
+      const key = this.getPublicIdentifier();
 
       this.skipInlineWS();
 
@@ -810,23 +856,39 @@ class RuntimeParser {
    * @private
    */
   getLiteral() {
-    const cc = this._source.charCodeAt(this._index);
-    if ((cc >= 48 && cc <= 57) || cc === 45) {
-      return this.getNumber();
-    } else if (cc === 34) { // "
-      return this.getString();
-    } else if (cc === 36) { // $
+    const cc0 = this._source.charCodeAt(this._index);
+
+    if (cc0 === 36) { // $
       this._index++;
       return {
         type: 'ext',
-        name: this.getIdentifier()
+        name: this.getPublicIdentifier()
       };
     }
 
-    return {
-      type: 'ref',
-      name: this.getIdentifier()
-    };
+    const cc1 = cc0 === 45 // -
+      // Peek at the next character after the dash.
+      ? this._source.charCodeAt(this._index + 1)
+      // Or keep using the character at the current index.
+      : cc0;
+
+    if ((cc1 >= 97 && cc1 <= 122) || // a-z
+        (cc1 >= 65 && cc1 <= 90)) { // A-Z
+      return {
+        type: 'ref',
+        name: this.getPrivateIdentifier()
+      };
+    }
+
+    if ((cc1 >= 48 && cc1 <= 57)) { // 0-9
+      return this.getNumber();
+    }
+
+    if (cc0 === 34) { // "
+      return this.getString();
+    }
+
+    throw this.error('Expected literal');
   }
 
   /**
@@ -886,7 +948,7 @@ class RuntimeParser {
 
         if ((cc >= 97 && cc <= 122) || // a-z
             (cc >= 65 && cc <= 90) || // A-Z
-             cc === 95 || cc === 47 || cc === 91) { // _/[
+             cc === 47 || cc === 91) { // /[
           this._index = start;
           return;
         }
diff --git a/fluent/src/resolver.js b/fluent/src/resolver.js
index 17f9f8005..d3dfa59e7 100644
--- a/fluent/src/resolver.js
+++ b/fluent/src/resolver.js
@@ -98,7 +98,9 @@ function DefaultMember(env, members, def) {
  */
 function MessageReference(env, {name}) {
   const { ctx, errors } = env;
-  const message = ctx.getMessage(name);
+  const message = name.startsWith('-')
+    ? ctx._privateMessages.get(name)
+    : ctx._publicMessages.get(name);
 
   if (!message) {
     errors.push(new ReferenceError(`Unknown message: ${name}`));
diff --git a/fluent/test/context_test.js b/fluent/test/context_test.js
index f8860eaa2..b547bb8e3 100644
--- a/fluent/test/context_test.js
+++ b/fluent/test/context_test.js
@@ -17,27 +17,48 @@ suite('Context', function() {
       ctx = new MessageContext('en-US', { useIsolating: false });
       ctx.addMessages(ftl`
         foo = Foo
-        bar = Bar
+        -bar = Private Bar
       `);
     });
 
+    test('adds messages', function() {
+      assert.equal(ctx._publicMessages.has('foo'), true);
+      assert.equal(ctx._privateMessages.has('foo'), false);
+      assert.equal(ctx._publicMessages.has('-bar'), false);
+      assert.equal(ctx._privateMessages.has('-bar'), true);
+    });
+
     test('preserves existing messages when new are added', function() {
       ctx.addMessages(ftl`
         baz = Baz
       `);
-      assert(ctx.hasMessage('foo'));
-      assert(ctx.hasMessage('bar'));
-      assert(ctx.hasMessage('baz'));
+
+      assert.equal(ctx._publicMessages.has('foo'), true);
+      assert.equal(ctx._privateMessages.has('foo'), false);
+      assert.equal(ctx._publicMessages.has('-bar'), false);
+      assert.equal(ctx._privateMessages.has('-bar'), true);
+
+      assert.equal(ctx._publicMessages.has('baz'), true);
+      assert.equal(ctx._privateMessages.has('baz'), false);
     });
 
+    test('public and private can share the same name', function() {
+      ctx.addMessages(ftl`
+        -foo = Private Foo
+      `);
+      assert.equal(ctx._publicMessages.has('foo'), true);
+      assert.equal(ctx._privateMessages.has('foo'), false);
+      assert.equal(ctx._publicMessages.has('-foo'), false);
+      assert.equal(ctx._privateMessages.has('-foo'), true);
+    });
+
+
     test('overwrites existing messages if the ids are the same', function() {
       ctx.addMessages(ftl`
         foo = New Foo
       `);
-      assert(ctx.hasMessage('foo'));
-      assert(ctx.hasMessage('bar'));
-      assert(ctx.hasMessage('baz'));
-      assert.equal(ctx._messages.size, 3);
+
+      assert.equal(ctx._publicMessages.size, 2);
 
       const msg = ctx.getMessage('foo');
       const val = ctx.format(msg, args, errs);
@@ -46,4 +67,44 @@ suite('Context', function() {
     });
   });
 
+  suite('hasMessage', function(){
+    suiteSetup(function() {
+      ctx = new MessageContext('en-US', { useIsolating: false });
+      ctx.addMessages(ftl`
+        foo = Foo
+        -bar = Private Bar
+      `);
+    });
+
+    test('returns true only for public messages', function() {
+      assert.equal(ctx.hasMessage('foo'), true);
+    });
+
+    test('returns false for private and missing messages', function() {
+      assert.equal(ctx.hasMessage('-bar'), false);
+      assert.equal(ctx.hasMessage('baz'), false);
+      assert.equal(ctx.hasMessage('-baz'), false);
+    });
+  });
+
+  suite('getMessage', function(){
+    suiteSetup(function() {
+      ctx = new MessageContext('en-US', { useIsolating: false });
+      ctx.addMessages(ftl`
+        foo = Foo
+        -bar = Private Bar
+      `);
+    });
+
+    test('returns public messages', function() {
+      assert.equal(ctx.getMessage('foo'), 'Foo');
+    });
+
+    test('returns null for private and missing messages', function() {
+      assert.equal(ctx.getMessage('-bar'), null);
+      assert.equal(ctx.getMessage('baz'), null);
+      assert.equal(ctx.getMessage('-baz'), null);
+    });
+  });
+
 });
diff --git a/fluent/test/fixtures_structure/private_message.json b/fluent/test/fixtures_structure/private_message.json
index 0967ef424..1c3364dd6 100644
--- a/fluent/test/fixtures_structure/private_message.json
+++ b/fluent/test/fixtures_structure/private_message.json
@@ -1 +1,105 @@
-{}
+{
+  "-brand-name": {
+    "val": [
+      {
+        "type": "sel",
+        "exp": null,
+        "vars": [
+          {
+            "key": {
+              "type": "varname",
+              "name": "nominative"
+            },
+            "val": "Firefox"
+          },
+          {
+            "key": {
+              "type": "varname",
+              "name": "accusative"
+            },
+            "val": "Firefoxa"
+          }
+        ],
+        "def": 0
+      }
+    ],
+    "attrs": {
+      "gender": "masculine"
+    }
+  },
+  "update-command": {
+    "val": [
+      "Zaktualizuj ",
+      {
+        "type": "var",
+        "id": {
+          "type": "ref",
+          "name": "-brand-name"
+        },
+        "key": {
+          "type": "varname",
+          "name": "accusative"
+        }
+      },
+      "."
+    ]
+  },
+  "update-successful": {
+    "val": [
+      {
+        "type": "sel",
+        "exp": {
+          "type": "attr",
+          "id": {
+            "type": "ref",
+            "name": "-brand-name"
+          },
+          "name": "gender"
+        },
+        "vars": [
+          {
+            "key": {
+              "type": "varname",
+              "name": "masculine"
+            },
+            "val": [
+              {
+                "type": "ref",
+                "name": "-brand-name"
+              },
+              " został pomyślnie zaktualizowany."
+            ]
+          },
+          {
+            "key": {
+              "type": "varname",
+              "name": "feminine"
+            },
+            "val": [
+              {
+                "type": "ref",
+                "name": "-brand-name"
+              },
+              " została pomyślnie zaktualizowana."
+            ]
+          },
+          {
+            "key": {
+              "type": "varname",
+              "name": "other"
+            },
+            "val": [
+              "Program ",
+              {
+                "type": "ref",
+                "name": "-brand-name"
+              },
+              " został pomyślnie zaktualizowany."
+            ]
+          }
+        ],
+        "def": 2
+      }
+    ]
+  }
+}
diff --git a/fluent/test/patterns_test.js b/fluent/test/patterns_test.js
index 316a5096a..352410af7 100644
--- a/fluent/test/patterns_test.js
+++ b/fluent/test/patterns_test.js
@@ -33,26 +33,45 @@ suite('Patterns', function(){
       ctx = new MessageContext('en-US', { useIsolating: false });
       ctx.addMessages(ftl`
         foo = Foo
-        bar = { foo } Bar
-        baz = { missing }
-        qux = { malformed
+        -bar = Bar
+
+        ref-public = { foo }
+        ref-private = { -bar }
+
+        ref-missing-public = { missing }
+        ref-missing-private = { -missing }
+
+        ref-malformed = { malformed
       `);
     });
 
-    test('returns the value', function(){
-      const msg = ctx.getMessage('bar');
+    test('resolves the reference to a public message', function(){
+      const msg = ctx.getMessage('ref-public');
+      const val = ctx.format(msg, args, errs);
+      assert.strictEqual(val, 'Foo');
+      assert.equal(errs.length, 0);
+    });
+
+    test('resolves the reference to a private message', function(){
+      const msg = ctx.getMessage('ref-private');
       const val = ctx.format(msg, args, errs);
-      assert.strictEqual(val, 'Foo Bar');
+      assert.strictEqual(val, 'Bar');
       assert.equal(errs.length, 0);
     });
 
-    test('returns the raw string if the referenced message is ' +
-       'not found', function(){
-      const msg = ctx.getMessage('baz');
+    test('returns the id if a public reference is missing', function(){
+      const msg = ctx.getMessage('ref-missing-public');
       const val = ctx.format(msg, args, errs);
       assert.strictEqual(val, 'missing');
       assert.ok(errs[0] instanceof ReferenceError); // unknown message
     });
+
+    test('returns the id if a private reference is missing', function(){
+      const msg = ctx.getMessage('ref-missing-private');
+      const val = ctx.format(msg, args, errs);
+      assert.strictEqual(val, '-missing');
+      assert.ok(errs[0] instanceof ReferenceError); // unknown message
+    });
   });
 
   suite('Complex string referencing a message with null value', function(){
@@ -125,10 +144,11 @@ suite('Patterns', function(){
     suiteSetup(function() {
       ctx = new MessageContext('en-US', { useIsolating: false });
       ctx.addMessages(ftl`
-        foo = { $sel ->
-           *[a] { foo }
-            [b] Bar
-        }
+        foo =
+            { $sel ->
+               *[a] { foo }
+                [b] Bar
+            }
         bar = { foo }
       `);
     });
@@ -152,11 +172,14 @@ suite('Patterns', function(){
     suiteSetup(function() {
       ctx = new MessageContext('en-US', { useIsolating: false });
       ctx.addMessages(ftl`
-        foo = { ref-foo ->
-           *[a] Foo
-        }
-
-        ref-foo = { foo }
+        -foo =
+            { -bar.attr ->
+               *[a] Foo
+            }
+        -bar
+            .attr = { -foo }
+
+        foo = { -foo }
       `);
     });
 
@@ -172,14 +195,20 @@ suite('Patterns', function(){
     suiteSetup(function() {
       ctx = new MessageContext('en-US', { useIsolating: false });
       ctx.addMessages(ftl`
-        foo = { foo ->
-           *[a] Foo
-        }
-
-        bar = { bar.attr ->
-           *[a] Bar
-        }
+        -foo =
+            { -bar.attr ->
+               *[a] Foo
+            }
             .attr = a
+
+        -bar =
+            { -foo.attr ->
+              *[a] Bar
+            }
+            .attr = { -foo }
+
+        foo = { -foo }
+        bar = { -bar }
       `);
     });
 
diff --git a/fluent/test/primitives_test.js b/fluent/test/primitives_test.js
index 682652729..2a0fb4aff 100644
--- a/fluent/test/primitives_test.js
+++ b/fluent/test/primitives_test.js
@@ -57,7 +57,10 @@ suite('Primitives', function() {
 
         placeable-attr   = { bar.attr }
 
-        selector-attr    = { bar.attr ->
+        -baz
+            .attr = Bar Attribute
+
+        selector-attr    = { -baz.attr ->
            *[Bar Attribute] Member 3
         }
       `);
diff --git a/fluent/test/select_expressions_test.js b/fluent/test/select_expressions_test.js
index 249698cab..7c3fabc76 100644
--- a/fluent/test/select_expressions_test.js
+++ b/fluent/test/select_expressions_test.js
@@ -50,11 +50,11 @@ suite('Select expressions', function() {
     });
   });
 
-  suite('with an invalid selector', function(){
+  suite('with a missing selector', function(){
     suiteSetup(function() {
       ctx = new MessageContext('en-US', { useIsolating: false });
       ctx.addMessages(ftl`
-        foo = { bar ->
+        foo = { $none ->
            *[a] A
             [b] B
         }
@@ -66,7 +66,7 @@ suite('Select expressions', function() {
       const val = ctx.format(msg, args, errs);
       assert.equal(val, 'A');
       assert.equal(errs.length, 1);
-      assert(errs[0] instanceof ReferenceError); // unknown message
+      assert(errs[0] instanceof ReferenceError); // unknown external
     });
   });