diff --git a/modules/@angular/compiler/src/i18n/extractor.ts b/modules/@angular/compiler/src/i18n/extractor.ts
new file mode 100644
index 0000000000..4f2908826a
--- /dev/null
+++ b/modules/@angular/compiler/src/i18n/extractor.ts
@@ -0,0 +1,264 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {HtmlAst, HtmlAstVisitor, HtmlAttrAst, HtmlCommentAst, HtmlElementAst, HtmlExpansionAst, HtmlExpansionCaseAst, HtmlTextAst} from '../html_ast';
+import {I18nError, I18N_ATTR_PREFIX, getI18nAttr, meaning, description, isOpeningComment, isClosingComment,} from './shared';
+import {htmlVisitAll} from '@angular/compiler/src/html_ast';
+
+export function extractAstMessages(
+    sourceAst: HtmlAst[], implicitTags: string[],
+    implicitAttrs: {[k: string]: string[]}): ExtractionResult {
+  const visitor = new _ExtractVisitor(implicitTags, implicitAttrs);
+  return visitor.extract(sourceAst);
+}
+
+export class ExtractionResult {
+  constructor(public messages: AstMessage[], public errors: I18nError[]) {}
+}
+
+class _ExtractVisitor implements HtmlAstVisitor {
+  // <el i18n>...</el>
+  private _inI18nNode = false;
+  private _depth: number = 0;
+
+  // <!--i18n-->...<!--/i18n-->
+  private _blockMeaningAndDesc: string;
+  private _blockChildren: HtmlAst[];
+  private _blockStartDepth: number;
+  private _inI18nBlock: boolean;
+
+  // {<icu message>}
+  private _inIcu = false;
+
+  private _sectionStartIndex: number;
+  private _errors: I18nError[];
+
+  constructor(private _implicitTags: string[], private _implicitAttrs: {[k: string]: string[]}) {}
+
+  extract(source: HtmlAst[]): ExtractionResult {
+    const messages: AstMessage[] = [];
+    this._inI18nBlock = false;
+    this._inI18nNode = false;
+    this._depth = 0;
+    this._inIcu = false;
+    this._sectionStartIndex = void 0;
+    this._errors = [];
+
+    source.forEach(node => node.visit(this, messages));
+
+    if (this._inI18nBlock) {
+      this._reportError(source[source.length - 1], 'Unclosed block');
+    }
+
+    return new ExtractionResult(messages, this._errors);
+  }
+
+  visitExpansionCase(part: HtmlExpansionCaseAst, messages: AstMessage[]): any {
+    htmlVisitAll(this, part.expression, messages);
+  }
+
+  visitExpansion(icu: HtmlExpansionAst, messages: AstMessage[]): any {
+    this._mayBeAddBlockChildren(icu);
+
+    const wasInIcu = this._inIcu;
+
+    if (!this._inIcu) {
+      if (this._inI18nNode || this._inI18nBlock) {
+        this._addMessage(messages, [icu]);
+      }
+      this._inIcu = true;
+    }
+
+    htmlVisitAll(this, icu.cases, messages);
+
+    this._inIcu = wasInIcu;
+  }
+
+  visitComment(comment: HtmlCommentAst, messages: AstMessage[]): any {
+    const isOpening = isOpeningComment(comment);
+
+    if (isOpening && (this._inI18nBlock || this._inI18nNode)) {
+      this._reportError(comment, 'Could not start a block inside a translatable section');
+      return;
+    }
+
+    const isClosing = isClosingComment(comment);
+
+    if (isClosing && !this._inI18nBlock) {
+      this._reportError(comment, 'Trying to close an unopened block');
+      return;
+    }
+
+    if (!(this._inI18nNode || this._inIcu)) {
+      if (!this._inI18nBlock) {
+        if (isOpening) {
+          this._inI18nBlock = true;
+          this._blockStartDepth = this._depth;
+          this._blockChildren = [];
+          this._blockMeaningAndDesc = comment.value.replace(/^i18n:?/, '').trim();
+          this._startSection(messages);
+        }
+      } else {
+        if (isClosing) {
+          if (this._depth == this._blockStartDepth) {
+            this._endSection(messages, this._blockChildren);
+            this._inI18nBlock = false;
+            this._addMessage(messages, this._blockChildren, this._blockMeaningAndDesc);
+          } else {
+            this._reportError(comment, 'I18N blocks should not cross element boundaries');
+            return;
+          }
+        }
+      }
+    }
+  }
+
+  visitText(text: HtmlTextAst, messages: AstMessage[]): any { this._mayBeAddBlockChildren(text); }
+
+  visitElement(el: HtmlElementAst, messages: AstMessage[]): any {
+    this._mayBeAddBlockChildren(el);
+    this._depth++;
+    const wasInI18nNode = this._inI18nNode;
+    let useSection = false;
+
+    // Extract only top level nodes with the (implicit) "i18n" attribute if not in a block or an ICU
+    // message
+    const i18nAttr = getI18nAttr(el);
+    const isImplicitI18n =
+        this._implicitTags.some((tagName: string): boolean => el.name === tagName);
+    if (!(this._inI18nNode || this._inIcu || this._inI18nBlock)) {
+      if (i18nAttr) {
+        this._inI18nNode = true;
+        this._addMessage(messages, el.children, i18nAttr.value);
+        useSection = true;
+      } else if (isImplicitI18n) {
+        this._inI18nNode = true;
+        this._addMessage(messages, el.children);
+      }
+    } else {
+      if (i18nAttr || isImplicitI18n) {
+        // TODO(vicb): we should probably allow nested implicit element (ie <div>)
+        this._reportError(
+            el, 'Could not mark an element as translatable inside a translatable section');
+      }
+    }
+
+    this._extractFromAttributes(el, messages);
+
+    if (useSection) {
+      this._startSection(messages);
+      htmlVisitAll(this, el.children, messages);
+      this._endSection(messages, el.children);
+    } else {
+      htmlVisitAll(this, el.children, messages);
+    }
+
+    this._depth--;
+    this._inI18nNode = wasInI18nNode;
+  }
+
+  visitAttr(ast: HtmlAttrAst, messages: AstMessage[]): any { throw new Error('unreachable code'); }
+
+  private _extractFromAttributes(el: HtmlElementAst, messages: AstMessage[]): void {
+    const explicitAttrNameToValue: Map<string, string> = new Map();
+    const implicitAttrNames: string[] = this._implicitAttrs[el.name] || [];
+
+    el.attrs.filter(attr => attr.name.startsWith(I18N_ATTR_PREFIX))
+        .forEach(
+            attr => explicitAttrNameToValue.set(
+                attr.name.substring(I18N_ATTR_PREFIX.length), attr.value));
+
+    el.attrs.forEach(attr => {
+      if (explicitAttrNameToValue.has(attr.name)) {
+        this._addMessage(messages, [attr], explicitAttrNameToValue.get(attr.name));
+      } else if (implicitAttrNames.some(name => attr.name === name)) {
+        this._addMessage(messages, [attr]);
+      }
+    });
+  }
+
+  private _addMessage(messages: AstMessage[], ast: HtmlAst[], meaningAndDesc?: string): void {
+    if (ast.length == 0 ||
+        ast.length == 1 && ast[0] instanceof HtmlAttrAst && !(<HtmlAttrAst>ast[0]).value) {
+      // Do not create empty messages
+      return;
+    }
+    messages.push(new AstMessage(ast, meaning(meaningAndDesc), description(meaningAndDesc)));
+  }
+
+  /**
+   * Add the node as a child of the block when:
+   * - we are in a block,
+   * - we are not inside a ICU message (those are handled separately),
+   * - the node is a "direct child" of the block
+   */
+  private _mayBeAddBlockChildren(ast: HtmlAst): void {
+    if (this._inI18nBlock && !this._inIcu && this._depth == this._blockStartDepth) {
+      this._blockChildren.push(ast);
+    }
+  }
+
+  /**
+   * Marks the start of a section, see `_endSection`
+   */
+  private _startSection(messages: AstMessage[]): void {
+    if (this._sectionStartIndex !== void 0) {
+      throw new Error('Unexpected section start');
+    }
+
+    this._sectionStartIndex = messages.length;
+  }
+
+  /**
+   * Terminates a section.
+   *
+   * If a section has only one significant children (comments not significant) then we should not
+   * keep the message
+   * from this children:
+   *
+   * `<p i18n="meaning|description">{ICU message}</p>` would produce two messages:
+   * - one for the <p> content with meaning and description,
+   * - another one for the ICU message.
+   *
+   * In this case the last message is discarded as it contains less information (the AST is
+   * otherwise identical).
+   *
+   * Note that we should still keep messages extracted from attributes inside the section (ie in the
+   * ICU message here)
+   */
+  private _endSection(messages: AstMessage[], directChildren: HtmlAst[]): void {
+    if (this._sectionStartIndex === void 0) {
+      throw new Error('Unexpected section end');
+    }
+
+    const startIndex = this._sectionStartIndex;
+    const significantChildren: number = directChildren.reduce(
+        (count: number, node: HtmlAst): number => count + (node instanceof HtmlCommentAst ? 0 : 1),
+        0);
+
+    if (significantChildren == 1) {
+      for (let i = startIndex; i < messages.length; i++) {
+        let ast = messages[i].ast;
+        if (!(ast.length == 1 && ast[0] instanceof HtmlAttrAst)) {
+          messages.splice(i, 1);
+          break;
+        }
+      }
+    }
+
+    this._sectionStartIndex = void 0;
+  }
+
+  private _reportError(astNode: HtmlAst, msg: string): void {
+    this._errors.push(new I18nError(astNode.sourceSpan, msg));
+  }
+}
+
+export class AstMessage {
+  constructor(public ast: HtmlAst[], public meaning: string, public description: string) {}
+}
diff --git a/modules/@angular/compiler/src/i18n/shared.ts b/modules/@angular/compiler/src/i18n/shared.ts
index 89c80791df..d4036f8002 100644
--- a/modules/@angular/compiler/src/i18n/shared.ts
+++ b/modules/@angular/compiler/src/i18n/shared.ts
@@ -6,11 +6,13 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {normalizeBlank} from '../../../router-deprecated/src/facade/lang';
 import {Parser as ExpressionParser} from '../expression_parser/parser';
 import {StringWrapper, isBlank, isPresent} from '../facade/lang';
 import {HtmlAst, HtmlAstVisitor, HtmlAttrAst, HtmlCommentAst, HtmlElementAst, HtmlExpansionAst, HtmlExpansionCaseAst, HtmlTextAst, htmlVisitAll} from '../html_ast';
 import {InterpolationConfig} from '../interpolation_config';
 import {ParseError, ParseSourceSpan} from '../parse_util';
+
 import {Message} from './message';
 
 export const I18N_ATTR = 'i18n';
@@ -31,10 +33,10 @@ export function partition(nodes: HtmlAst[], errors: ParseError[], implicitTags:
     let node = nodes[i];
     let msgNodes: HtmlAst[] = [];
     // Nodes between `<!-- i18n -->` and `<!-- /i18n -->`
-    if (_isOpeningComment(node)) {
+    if (isOpeningComment(node)) {
       let i18n = (<HtmlCommentAst>node).value.replace(/^i18n:?/, '').trim();
 
-      while (++i < nodes.length && !_isClosingComment(nodes[i])) {
+      while (++i < nodes.length && !isClosingComment(nodes[i])) {
         msgNodes.push(nodes[i]);
       }
 
@@ -46,7 +48,7 @@ export function partition(nodes: HtmlAst[], errors: ParseError[], implicitTags:
       parts.push(new Part(null, null, msgNodes, i18n, true));
     } else if (node instanceof HtmlElementAst) {
       // Node with an `i18n` attribute
-      let i18n = _findI18nAttr(node);
+      let i18n = getI18nAttr(node);
       let hasI18n: boolean = isPresent(i18n) || implicitTags.indexOf(node.name) > -1;
       parts.push(new Part(node, null, node.children, isPresent(i18n) ? i18n.value : null, hasI18n));
     } else if (node instanceof HtmlTextAst) {
@@ -83,33 +85,27 @@ export class Part {
   }
 }
 
-function _isOpeningComment(n: HtmlAst): boolean {
+export function isOpeningComment(n: HtmlAst): boolean {
   return n instanceof HtmlCommentAst && isPresent(n.value) && n.value.startsWith('i18n');
 }
 
-function _isClosingComment(n: HtmlAst): boolean {
+export function isClosingComment(n: HtmlAst): boolean {
   return n instanceof HtmlCommentAst && isPresent(n.value) && n.value === '/i18n';
 }
 
-function _findI18nAttr(p: HtmlElementAst): HtmlAttrAst {
-  let attrs = p.attrs;
-  for (let i = 0; i < attrs.length; i++) {
-    if (attrs[i].name === I18N_ATTR) {
-      return attrs[i];
-    }
-  }
-  return null;
+export function getI18nAttr(p: HtmlElementAst): HtmlAttrAst {
+  return normalizeBlank(p.attrs.find(attr => attr.name === I18N_ATTR));
 }
 
 export function meaning(i18n: string): string {
-  if (isBlank(i18n) || i18n == '') return null;
+  if (isBlank(i18n) || i18n == '') return '';
   return i18n.split('|')[0];
 }
 
 export function description(i18n: string): string {
-  if (isBlank(i18n) || i18n == '') return null;
+  if (isBlank(i18n) || i18n == '') return '';
   let parts = i18n.split('|', 2);
-  return parts.length > 1 ? parts[1] : null;
+  return parts.length > 1 ? parts[1] : '';
 }
 
 /**
diff --git a/modules/@angular/compiler/test/html_ast_serializer_spec.ts b/modules/@angular/compiler/test/html_ast_serializer_spec.ts
index 30d19602af..4bb7a91083 100644
--- a/modules/@angular/compiler/test/html_ast_serializer_spec.ts
+++ b/modules/@angular/compiler/test/html_ast_serializer_spec.ts
@@ -3,7 +3,7 @@ import {HtmlParser} from '@angular/compiler/src/html_parser';
 import {beforeEach, ddescribe, describe, expect, it} from '@angular/core/testing/testing_internal';
 
 export function main() {
-  ddescribe('HtmlAst serilaizer', () => {
+  describe('HtmlAst serilaizer', () => {
     var parser: HtmlParser;
 
     beforeEach(() => { parser = new HtmlParser(); });
@@ -54,10 +54,10 @@ export function main() {
 
 class _SerializerVisitor implements HtmlAstVisitor {
   visitElement(ast: HtmlElementAst, context: any): any {
-    return `<${ast.name}${this._visitAll(ast.attrs)}>${this._visitAll(ast.children)}</${ast.name}>`;
+    return `<${ast.name}${this._visitAll(ast.attrs, ' ')}>${this._visitAll(ast.children)}</${ast.name}>`;
   }
 
-  visitAttr(ast: HtmlAttrAst, context: any): any { return ` ${ast.name}="${ast.value}"`; }
+  visitAttr(ast: HtmlAttrAst, context: any): any { return `${ast.name}="${ast.value}"`; }
 
   visitText(ast: HtmlTextAst, context: any): any { return ast.value; }
 
@@ -71,11 +71,16 @@ class _SerializerVisitor implements HtmlAstVisitor {
     return ` ${ast.value} {${this._visitAll(ast.expression)}}`;
   }
 
-  private _visitAll(ast: HtmlAst[]) { return ast.map(a => a.visit(this, null)).join(''); }
+  private _visitAll(ast: HtmlAst[], join: string = ''): string {
+    if (ast.length == 0) {
+      return '';
+    }
+    return join + ast.map(a => a.visit(this, null)).join(join);
+  }
 }
 
 const serializerVisitor = new _SerializerVisitor();
 
-export function serializeHtmlAst(ast: HtmlAst[]) {
+export function serializeHtmlAst(ast: HtmlAst[]): string[] {
   return ast.map(a => a.visit(serializerVisitor, null));
 }
diff --git a/modules/@angular/compiler/test/i18n/extractor_spec.ts b/modules/@angular/compiler/test/i18n/extractor_spec.ts
new file mode 100644
index 0000000000..55b196bce9
--- /dev/null
+++ b/modules/@angular/compiler/test/i18n/extractor_spec.ts
@@ -0,0 +1,295 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {HtmlParser} from '@angular/compiler/src/html_parser';
+import {ExtractionResult, extractAstMessages} from '@angular/compiler/src/i18n/extractor';
+import {beforeEach, ddescribe, describe, expect, iit, inject, it, xdescribe, xit} from '@angular/core/testing/testing_internal';
+
+import {serializeHtmlAst} from '../html_ast_serializer_spec'
+
+export function main() {
+  ddescribe(
+      'MessageExtractor',
+      () => {
+        function getExtractionResult(
+            html: string, implicitTags: string[],
+            implicitAttrs: {[k: string]: string[]}): ExtractionResult {
+          const htmlParser = new HtmlParser();
+          const parseResult = htmlParser.parse(html, 'extractor spec', true);
+          if (parseResult.errors.length > 1) {
+            throw Error(`unexpected parse errors: ${parseResult.errors.join('\n')}`);
+          }
+
+          return extractAstMessages(parseResult.rootNodes, implicitTags, implicitAttrs);
+        }
+
+        function extract(
+            html: string, implicitTags: string[] = [],
+            implicitAttrs: {[k: string]: string[]} = {}): [string[], string, string][] {
+          const messages = getExtractionResult(html, implicitTags, implicitAttrs).messages;
+
+          // clang-format off
+          // https://github.com/angular/clang-format/issues/35
+          return messages.map(
+              message => [serializeHtmlAst(message.ast), message.meaning, message.description, ]) as [string[], string, string][];
+          // clang-format on
+        }
+
+        function extractErrors(
+            html: string, implicitTags: string[] = [],
+            implicitAttrs: {[k: string]: string[]} = {}): any[] {
+          const errors = getExtractionResult(html, implicitTags, implicitAttrs).errors;
+
+          return errors.map((e): [string, string] => [e.msg, e.span.toString()]);
+        }
+
+        describe('elements', () => {
+          it('should extract from elements', () => {
+            expect(extract('<div i18n="m|d">text<span>nested</span></div>')).toEqual([
+              [['text', '<span>nested</span>'], 'm', 'd'],
+            ]);
+          });
+
+          it('should not create a message for empty elements',
+             () => { expect(extract('<div i18n="m|d"></div>')).toEqual([]); });
+        });
+
+        describe('blocks', () => {
+          it('should extract from blocks', () => {
+            expect(extract(`<!-- i18n: meaning1|desc1 -->message1<!-- /i18n -->
+         <!-- i18n: meaning2 -->message2<!-- /i18n -->
+         <!-- i18n -->message3<!-- /i18n -->`))
+                .toEqual([
+                  [['message1'], 'meaning1', 'desc1'],
+                  [['message2'], 'meaning2', ''],
+                  [['message3'], '', ''],
+                ]);
+          });
+
+          it('should extract all siblings', () => {
+            expect(
+                extract(
+                    `<!-- i18n -->text<p>html<b>nested</b></p>{count, plural, =0 {<span>html</span>}}{{interp}}<!-- /i18n -->`))
+                .toEqual([
+                  [['{count, plural, =0 {<span>html</span>}}'], '', ''],
+                  [
+                    [
+                      'text', '<p>html<b>nested</b></p>', '{count, plural, =0 {<span>html</span>}}',
+                      '{{interp}}'
+                    ],
+                    '', ''
+                  ],
+                ]);
+          });
+
+          it('should ignore other comments', () => {
+            expect(extract(`<!-- i18n: meaning1|desc1 --><!-- other -->message1<!-- /i18n -->`))
+                .toEqual([
+                  [['message1'], 'meaning1', 'desc1'],
+                ]);
+          });
+
+          it('should not create a message for empty blocks',
+             () => { expect(extract(`<!-- i18n: meaning1|desc1 --><!-- /i18n -->`)).toEqual([]); });
+        });
+
+        describe('ICU messages', () => {
+          it('should extract ICU messages from translatable elements', () => {
+            // single message when ICU is the only children
+            expect(extract('<div i18n="m|d">{count, plural, =0 {text}}</div>')).toEqual([
+              [['{count, plural, =0 {text}}'], 'm', 'd'],
+            ]);
+
+            // one message for the element content and one message for the ICU
+            expect(extract('<div i18n="m|d">before{count, plural, =0 {text}}after</div>')).toEqual([
+              [['before', '{count, plural, =0 {text}}', 'after'], 'm', 'd'],
+              [['{count, plural, =0 {text}}'], '', ''],
+            ]);
+          });
+
+          it('should extract ICU messages from translatable block', () => {
+            // single message when ICU is the only children
+            expect(extract('<!-- i18n:m|d -->{count, plural, =0 {text}}<!-- /i18n -->')).toEqual([
+              [['{count, plural, =0 {text}}'], 'm', 'd'],
+            ]);
+
+            // one message for the block content and one message for the ICU
+            expect(extract('<!-- i18n:m|d -->before{count, plural, =0 {text}}after<!-- /i18n -->'))
+                .toEqual([
+                  [['{count, plural, =0 {text}}'], '', ''],
+                  [['before', '{count, plural, =0 {text}}', 'after'], 'm', 'd'],
+                ]);
+          });
+
+          it('should not extract ICU messages outside of i18n sections',
+             () => { expect(extract('{count, plural, =0 {text}}')).toEqual([]); });
+
+          it('should not extract nested ICU messages', () => {
+            expect(extract('<div i18n="m|d">{count, plural, =0 { {sex, gender, =m {m}} }}</div>'))
+                .toEqual([
+                  [['{count, plural, =0 {{sex, gender, =m {m}} }}'], 'm', 'd'],
+                ]);
+          });
+        });
+
+        describe('attributes', () => {
+          it('should extract from attributes outside of translatable section', () => {
+            expect(extract('<div i18n-title="m|d" title="msg"></div>')).toEqual([
+              [['title="msg"'], 'm', 'd'],
+            ]);
+          });
+
+          it('should extract from attributes in translatable element', () => {
+            expect(extract('<div i18n><p><b i18n-title="m|d" title="msg"></b></p></div>')).toEqual([
+              [['<p><b i18n-title="m|d" title="msg"></b></p>'], '', ''],
+              [['title="msg"'], 'm', 'd'],
+            ]);
+          });
+
+          it('should extract from attributes in translatable block', () => {
+            expect(
+                extract('<!-- i18n --><p><b i18n-title="m|d" title="msg"></b></p><!-- /i18n -->'))
+                .toEqual([
+                  [['title="msg"'], 'm', 'd'],
+                  [['<p><b i18n-title="m|d" title="msg"></b></p>'], '', ''],
+                ]);
+          });
+
+          it('should extract from attributes in translatable ICU', () => {
+            expect(
+                extract(
+                    '<!-- i18n -->{count, plural, =0 {<p><b i18n-title="m|d" title="msg"></b></p>}}<!-- /i18n -->'))
+                .toEqual([
+                  [['title="msg"'], 'm', 'd'],
+                  [['{count, plural, =0 {<p><b i18n-title="m|d" title="msg"></b></p>}}'], '', ''],
+                ]);
+          });
+
+          it('should extract from attributes in non translatable ICU', () => {
+            expect(extract('{count, plural, =0 {<p><b i18n-title="m|d" title="msg"></b></p>}}'))
+                .toEqual([
+                  [['title="msg"'], 'm', 'd'],
+                ]);
+          });
+
+          it('should not create a message for empty attributes',
+             () => { expect(extract('<div i18n-title="m|d" title></div>')).toEqual([]); });
+        });
+
+        describe('implicit tags', () => {
+          it('should extract from implicit tags', () => {
+            expect(extract('<b>bold</b><i>italic</i>', ['b'])).toEqual([
+              [['bold'], '', ''],
+            ]);
+          });
+        });
+
+        describe('implicit attributes', () => {
+          it('should extract implicit attributes', () => {
+            expect(extract('<b title="bb">bold</b><i title="ii">italic</i>', [], {'b': ['title']}))
+                .toEqual([
+                  [['title="bb"'], '', ''],
+                ]);
+          });
+        });
+
+        describe('errors', () => {
+          describe('elements', () => {
+            it('should report nested translatable elements', () => {
+              expect(extractErrors(`<p i18n><b i18n></b></p>`)).toEqual([
+                [
+                  'Could not mark an element as translatable inside a translatable section',
+                  '<b i18n>'
+                ],
+              ]);
+            });
+
+            it('should report translatable elements in implicit elements', () => {
+              expect(extractErrors(`<p><b i18n></b></p>`, ['p'])).toEqual([
+                [
+                  'Could not mark an element as translatable inside a translatable section',
+                  '<b i18n>'
+                ],
+              ]);
+            });
+
+            it('should report translatable elements in translatable blocks', () => {
+              expect(extractErrors(`<!-- i18n --><b i18n></b><!-- /i18n -->`)).toEqual([
+                [
+                  'Could not mark an element as translatable inside a translatable section',
+                  '<b i18n>'
+                ],
+              ]);
+            });
+          });
+
+          describe('blocks', () => {
+            it('should report nested blocks', () => {
+              expect(extractErrors(`<!-- i18n --><!-- i18n --><!-- /i18n --><!-- /i18n -->`))
+                  .toEqual([
+                    ['Could not start a block inside a translatable section', '<!--'],
+                    ['Trying to close an unopened block', '<!--'],
+                  ]);
+
+            });
+
+            it('should report unclosed blocks', () => {
+              expect(extractErrors(`<!-- i18n -->`)).toEqual([
+                ['Unclosed block', '<!--'],
+              ]);
+            });
+
+            it('should report translatable blocks in translatable elements', () => {
+              expect(extractErrors(`<p i18n><!-- i18n --><!-- /i18n --></p>`)).toEqual([
+                ['Could not start a block inside a translatable section', '<!--'],
+                ['Trying to close an unopened block', '<!--'],
+              ]);
+            });
+
+            it('should report translatable blocks in implicit elements', () => {
+              expect(extractErrors(`<p><!-- i18n --><!-- /i18n --></p>`, ['p'])).toEqual([
+                ['Could not start a block inside a translatable section', '<!--'],
+                ['Trying to close an unopened block', '<!--'],
+              ]);
+            });
+
+            it('should report when start and end of a block are not at the same level', () => {
+              expect(extractErrors(`<!-- i18n --><p><!-- /i18n --></p>`)).toEqual([
+                ['I18N blocks should not cross element boundaries', '<!--'],
+                ['Unclosed block', '<p>'],
+              ]);
+
+              expect(extractErrors(`<p><!-- i18n --></p><!-- /i18n -->`)).toEqual([
+                ['I18N blocks should not cross element boundaries', '<!--'],
+                ['Unclosed block', '<!--'],
+              ]);
+            });
+          });
+
+          describe('implicit elements', () => {
+            it('should report nested implicit elements', () => {
+              expect(extractErrors(`<p><b></b></p>`, ['p', 'b'])).toEqual([
+                ['Could not mark an element as translatable inside a translatable section', '<b>'],
+              ]);
+            });
+
+            it('should report implicit element in translatable element', () => {
+              expect(extractErrors(`<p i18n><b></b></p>`, ['b'])).toEqual([
+                ['Could not mark an element as translatable inside a translatable section', '<b>'],
+              ]);
+            });
+
+            it('should report implicit element in translatable blocks', () => {
+              expect(extractErrors(`<!-- i18n --><b></b><!-- /i18n -->`, ['b'])).toEqual([
+                ['Could not mark an element as translatable inside a translatable section', '<b>'],
+              ]);
+            });
+          });
+        });
+      });
+}