diff --git a/xml/impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownTagInspection.java b/xml/impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownTagInspection.java
index 63e8ec9513f9..667d1e523f49 100644
--- a/xml/impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownTagInspection.java
+++ b/xml/impl/src/com/intellij/codeInspection/htmlInspections/HtmlUnknownTagInspection.java
@@ -200,8 +200,15 @@ public class HtmlUnknownTagInspection extends HtmlLocalInspectionTool {
     return descriptor == null || descriptor instanceof AnyXmlElementDescriptor;
   }
 
+  // this hack is needed, because we temporarily ignore svg and mathML namespaces
+  // todo: provide schemas for svg and mathML and remove this in IDEA XI
+  private static boolean isInSpecialHtml5Namespace(XmlTag tag) {
+    final String ns = tag.getNamespace();
+    return HtmlUtil.SVG_NAMESPACE.equals(ns) || HtmlUtil.MATH_ML_NAMESPACE.endsWith(ns);
+  }
+
   protected void checkTag(@NotNull final XmlTag tag, @NotNull final ProblemsHolder holder, final boolean isOnTheFly) {
-    if (!(tag instanceof HtmlTag) || !XmlHighlightVisitor.shouldBeValidated(tag)) {
+    if (!(tag instanceof HtmlTag) || !XmlHighlightVisitor.shouldBeValidated(tag) || isInSpecialHtml5Namespace(tag)) {
       return;
     }
 
diff --git a/xml/impl/src/com/intellij/javaee/InternalResourceProvider.java b/xml/impl/src/com/intellij/javaee/InternalResourceProvider.java
index e9482d48ae29..9c5a4d4ee306 100644
--- a/xml/impl/src/com/intellij/javaee/InternalResourceProvider.java
+++ b/xml/impl/src/com/intellij/javaee/InternalResourceProvider.java
@@ -15,13 +15,14 @@
  */
 package com.intellij.javaee;
 
+import com.intellij.xml.util.HtmlUtil;
 import com.intellij.xml.util.XmlUtil;
 
 /**
  * @author Dmitry Avdeev
  */
 public class InternalResourceProvider implements StandardResourceProvider{
-  
+
   public void registerResources(ResourceRegistrar registrar) {
     ResourceRegistrarImpl impl = (ResourceRegistrarImpl)registrar;
     
@@ -54,5 +55,8 @@ public class InternalResourceProvider implements StandardResourceProvider{
     impl.addInternalResource("http://www.wapforum.org/DTD/xhtml-mobile10-flat.dtd", "xhtml-mobile/xhtml-mobile10-flat.dtd");
     impl.addInternalResource("http://www.wapforum.org/DTD/xhtml-mobile12.dtd", "xhtml-mobile/xhtml-mobile12.dtd");
 
+    // svg and mathML
+    impl.addIgnoredResource(HtmlUtil.MATH_ML_NAMESPACE);
+    impl.addIgnoredResource(HtmlUtil.SVG_NAMESPACE);
   }
 }
diff --git a/xml/impl/src/com/intellij/psi/impl/source/html/HtmlTagImpl.java b/xml/impl/src/com/intellij/psi/impl/source/html/HtmlTagImpl.java
index f7e8c13b9f83..1d324137d85c 100644
--- a/xml/impl/src/com/intellij/psi/impl/source/html/HtmlTagImpl.java
+++ b/xml/impl/src/com/intellij/psi/impl/source/html/HtmlTagImpl.java
@@ -87,9 +87,18 @@ public class HtmlTagImpl extends XmlTagImpl implements HtmlTag {
 
   @NotNull
   public String getNamespace() {
-    if(getNamespacePrefix().length() == 0)
+    final String xmlNamespace = super.getNamespace();
+
+    if (getNamespacePrefix().length() > 0) {
+      return xmlNamespace;
+    }
+
+    if (xmlNamespace.length() == 0 || xmlNamespace.equals(XmlUtil.XHTML_URI)) {
       return XmlUtil.HTML_URI;
-    return super.getNamespace();
+    }
+
+    // ex.: mathML and SVG namespaces can be used inside html file
+    return xmlNamespace;
   }
 
   protected String getRealNs(final String value) {
diff --git a/xml/impl/src/com/intellij/xml/util/HtmlUtil.java b/xml/impl/src/com/intellij/xml/util/HtmlUtil.java
index 55b5e409a39d..948d6f78b84f 100644
--- a/xml/impl/src/com/intellij/xml/util/HtmlUtil.java
+++ b/xml/impl/src/com/intellij/xml/util/HtmlUtil.java
@@ -87,6 +87,9 @@ public class HtmlUtil {
             , "video/quicktime", "video/x-msvideo", "video/x-sgi-movie", "x-conference/x-cooltalk", "x-world/x-vrml"};
   @NonNls public static final String LINK = "link";
 
+  @NonNls public static final String MATH_ML_NAMESPACE = "http://www.w3.org/1998/Math/MathML";
+  @NonNls public static final String SVG_NAMESPACE = "http://www.w3.org/2000/svg";
+
   private HtmlUtil() {}
   @NonNls private static final String[] EMPTY_TAGS = {
     "base","hr","meta","link","frame","br","basefont","param","img","area","input","isindex","col", /*html 5*/ "source","wbr"