diff --git a/packages/compiler/src/i18n/serializers/xliff.ts b/packages/compiler/src/i18n/serializers/xliff.ts
index 11a59441a6..fb64794daa 100644
--- a/packages/compiler/src/i18n/serializers/xliff.ts
+++ b/packages/compiler/src/i18n/serializers/xliff.ts
@@ -20,9 +20,11 @@ const _XMLNS = 'urn:oasis:names:tc:xliff:document:1.2';
 // TODO(vicb): make this a param (s/_/-/)
 const _DEFAULT_SOURCE_LANG = 'en';
 const _PLACEHOLDER_TAG = 'x';
+const _MARKER_TAG = 'mrk';
 
 const _FILE_TAG = 'file';
 const _SOURCE_TAG = 'source';
+const _SEGMENT_SOURCE_TAG = 'seg-source';
 const _TARGET_TAG = 'target';
 const _UNIT_TAG = 'trans-unit';
 const _CONTEXT_GROUP_TAG = 'context-group';
@@ -214,8 +216,9 @@ class XliffParser implements ml.Visitor {
         }
         break;
 
+      // ignore those tags
       case _SOURCE_TAG:
-        // ignore source message
+      case _SEGMENT_SOURCE_TAG:
         break;
 
       case _TARGET_TAG:
@@ -266,7 +269,7 @@ class XmlToI18n implements ml.Visitor {
 
     const i18nNodes = this._errors.length > 0 || xmlIcu.rootNodes.length == 0 ?
         [] :
-        ml.visitAll(this, xmlIcu.rootNodes);
+        [].concat(...ml.visitAll(this, xmlIcu.rootNodes));
 
     return {
       i18nNodes: i18nNodes,
@@ -276,7 +279,7 @@ class XmlToI18n implements ml.Visitor {
 
   visitText(text: ml.Text, context: any) { return new i18n.Text(text.value, text.sourceSpan !); }
 
-  visitElement(el: ml.Element, context: any): i18n.Placeholder|null {
+  visitElement(el: ml.Element, context: any): i18n.Placeholder|ml.Node[]|null {
     if (el.name === _PLACEHOLDER_TAG) {
       const nameAttr = el.attrs.find((attr) => attr.name === 'id');
       if (nameAttr) {
@@ -284,9 +287,14 @@ class XmlToI18n implements ml.Visitor {
       }
 
       this._addError(el, `<${_PLACEHOLDER_TAG}> misses the "id" attribute`);
-    } else {
-      this._addError(el, `Unexpected tag`);
+      return null;
     }
+
+    if (el.name === _MARKER_TAG) {
+      return [].concat(...ml.visitAll(this, el.children));
+    }
+
+    this._addError(el, `Unexpected tag`);
     return null;
   }
 
diff --git a/packages/compiler/src/i18n/serializers/xliff2.ts b/packages/compiler/src/i18n/serializers/xliff2.ts
index ea754b34fc..eac6612f5d 100644
--- a/packages/compiler/src/i18n/serializers/xliff2.ts
+++ b/packages/compiler/src/i18n/serializers/xliff2.ts
@@ -21,6 +21,7 @@ const _XMLNS = 'urn:oasis:names:tc:xliff:document:2.0';
 const _DEFAULT_SOURCE_LANG = 'en';
 const _PLACEHOLDER_TAG = 'ph';
 const _PLACEHOLDER_SPANNING_TAG = 'pc';
+const _MARKER_TAG = 'mrk';
 
 const _XLIFF_TAG = 'xliff';
 const _SOURCE_TAG = 'source';
@@ -332,6 +333,8 @@ class XmlToI18n implements ml.Visitor {
               new i18n.Placeholder('', endId, el.sourceSpan));
         }
         break;
+      case _MARKER_TAG:
+        return [].concat(...ml.visitAll(this, el.children));
       default:
         this._addError(el, `Unexpected tag`);
     }
diff --git a/packages/compiler/test/i18n/serializers/xliff2_spec.ts b/packages/compiler/test/i18n/serializers/xliff2_spec.ts
index 937dcf0eb8..027bdc5bdc 100644
--- a/packages/compiler/test/i18n/serializers/xliff2_spec.ts
+++ b/packages/compiler/test/i18n/serializers/xliff2_spec.ts
@@ -238,6 +238,24 @@ lines</source>
 lignes</target>
       </segment>
     </unit>
+    <unit id="mrk-test">
+     <notes>
+      <note id="n1" appliesTo="target">Please check the translation for 'namespace'. On also can use 'espace de nom',but I think most technical manuals use the English term.</note>
+     </notes>
+     <segment>
+      <source>You use your own namespace.</source>
+      <target>Vous pouvez utiliser votre propre <mrk id="m1" type="comment" ref="#n1">namespace</mrk>.</target>
+     </segment>
+    </unit>
+    <unit id="mrk-test2">
+     <notes>
+      <note id="n1" appliesTo="target">Please check the translation for 'namespace'. On also can use 'espace de nom',but I think most technical manuals use the English term.</note>
+     </notes>
+     <segment>
+      <source>You use your own namespace.</source>
+      <target>Vous pouvez utiliser <mrk id="m1" type="comment" ref="#n1">votre propre <mrk id="m2" type="comment" ref="#n1">namespace</mrk></mrk>.</target>
+     </segment>
+    </unit>
   </file>
 </xliff>
 `;
@@ -289,7 +307,9 @@ lignes</target>
           '5229984852258993423': '{VAR_PLURAL, plural, =0 {[{VAR_SELECT, select, other {[<ph' +
               ' name="START_PARAGRAPH"/>, profondément imbriqué, <ph name="CLOSE_PARAGRAPH"/>]}},  ]}, =other {[beaucoup]}}',
           '2340165783990709777': `multi
-lignes`
+lignes`,
+          'mrk-test': 'Vous pouvez utiliser votre propre namespace.',
+          'mrk-test2': 'Vous pouvez utiliser votre propre namespace.'
         });
       });
 
diff --git a/packages/compiler/test/i18n/serializers/xliff_spec.ts b/packages/compiler/test/i18n/serializers/xliff_spec.ts
index 010bace00d..87c153b633 100644
--- a/packages/compiler/test/i18n/serializers/xliff_spec.ts
+++ b/packages/compiler/test/i18n/serializers/xliff_spec.ts
@@ -221,6 +221,20 @@ lignes</target>
           <context context-type="linenumber">12</context>
         </context-group>
       </trans-unit>
+      <trans-unit id="mrk-test">
+        <source>First sentence.</source>
+        <seg-source>
+          <invalid-tag>Should not be parsed</invalid-tag>
+        </seg-source>
+        <target>Translated <mrk mtype="seg" mid="1">first sentence</mrk>.</target>
+      </trans-unit>
+      <trans-unit id="mrk-test2">
+        <source>First sentence. Second sentence.</source>
+        <seg-source>
+          <invalid-tag>Should not be parsed</invalid-tag>
+        </seg-source>
+        <target>Translated <mrk mtype="seg" mid="1"><mrk mtype="seg" mid="2">first</mrk> sentence</mrk>.</target>
+      </trans-unit>
     </body>
   </file>
 </xliff>
@@ -273,7 +287,9 @@ lignes</target>
               '{VAR_PLURAL, plural, =0 {[{VAR_SELECT, select, other {[<ph' +
               ' name="START_PARAGRAPH"/>, profondément imbriqué, <ph name="CLOSE_PARAGRAPH"/>]}},  ]}, =other {[beaucoup]}}',
           'fcfa109b0e152d4c217dbc02530be0bcb8123ad1': `multi
-lignes`
+lignes`,
+          'mrk-test': 'Translated first sentence.',
+          'mrk-test2': 'Translated first sentence.'
         });
       });