diff --git a/libraries/stdlib/js/idl/org.w3c.css.masking.idl b/libraries/stdlib/js/idl/org.w3c.css.masking.idl
new file mode 100644
index 00000000000..2849bd7aeb4
--- /dev/null
+++ b/libraries/stdlib/js/idl/org.w3c.css.masking.idl
@@ -0,0 +1,21 @@
+namespace org.w3c.css.masking;
+
+
+// Downloaded from https://www.w3.org/TR/css-masking-1/
+interface SVGClipPathElement : SVGElement {
+readonly attribute SVGAnimatedEnumeration clipPathUnits;
+readonly attribute SVGAnimatedTransformList transform;
+};
+
+SVGClipPathElement implements SVGUnitTypes;
+interface SVGMaskElement : SVGElement {
+readonly attribute SVGAnimatedEnumeration maskUnits;
+readonly attribute SVGAnimatedEnumeration maskContentUnits;
+readonly attribute SVGAnimatedLength x;
+readonly attribute SVGAnimatedLength y;
+readonly attribute SVGAnimatedLength width;
+readonly attribute SVGAnimatedLength height;
+};
+
+SVGMaskElement implements SVGUnitTypes;
+
diff --git a/libraries/stdlib/js/src/org.w3c/org.khronos.webgl.kt b/libraries/stdlib/js/src/org.w3c/org.khronos.webgl.kt
index dd44dca6613..d7133ab7348 100644
--- a/libraries/stdlib/js/src/org.w3c/org.khronos.webgl.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.khronos.webgl.kt
@@ -10,6 +10,7 @@
 package org.khronos.webgl
 
 import kotlin.js.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.css.masking.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.css.masking.kt
new file mode 100644
index 00000000000..c462d627ee5
--- /dev/null
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.css.masking.kt
@@ -0,0 +1,59 @@
+/*
+ * Copyright 2010-2018 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license 
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+// NOTE: THIS FILE IS AUTO-GENERATED, DO NOT EDIT!
+// See libraries/tools/idl2k for details
+
+@file:Suppress("NESTED_CLASS_IN_EXTERNAL_INTERFACE")
+package org.w3c.css.masking
+
+import kotlin.js.*
+import org.khronos.webgl.*
+import org.w3c.dom.*
+import org.w3c.dom.css.*
+import org.w3c.dom.events.*
+import org.w3c.dom.parsing.*
+import org.w3c.dom.pointerevents.*
+import org.w3c.dom.svg.*
+import org.w3c.dom.url.*
+import org.w3c.fetch.*
+import org.w3c.files.*
+import org.w3c.notifications.*
+import org.w3c.performance.*
+import org.w3c.workers.*
+import org.w3c.xhr.*
+
+/**
+ * Exposes the JavaScript [SVGClipPathElement](https://developer.mozilla.org/en/docs/Web/API/SVGClipPathElement) to Kotlin
+ */
+public external abstract class SVGClipPathElement : SVGElement, SVGUnitTypes {
+    open val clipPathUnits: SVGAnimatedEnumeration
+    open val transform: SVGAnimatedTransformList
+
+    companion object {
+        val SVG_UNIT_TYPE_UNKNOWN: Short
+        val SVG_UNIT_TYPE_USERSPACEONUSE: Short
+        val SVG_UNIT_TYPE_OBJECTBOUNDINGBOX: Short
+    }
+}
+
+/**
+ * Exposes the JavaScript [SVGMaskElement](https://developer.mozilla.org/en/docs/Web/API/SVGMaskElement) to Kotlin
+ */
+public external abstract class SVGMaskElement : SVGElement, SVGUnitTypes {
+    open val maskUnits: SVGAnimatedEnumeration
+    open val maskContentUnits: SVGAnimatedEnumeration
+    open val x: SVGAnimatedLength
+    open val y: SVGAnimatedLength
+    open val width: SVGAnimatedLength
+    open val height: SVGAnimatedLength
+
+    companion object {
+        val SVG_UNIT_TYPE_UNKNOWN: Short
+        val SVG_UNIT_TYPE_USERSPACEONUSE: Short
+        val SVG_UNIT_TYPE_OBJECTBOUNDINGBOX: Short
+    }
+}
+
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.css.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.css.kt
index 556b5d4c362..4dea0f510a8 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.css.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.css.kt
@@ -11,6 +11,7 @@ package org.w3c.dom.css
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.events.*
 import org.w3c.dom.parsing.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.events.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.events.kt
index a76c57ad41b..28814b80b4c 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.events.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.events.kt
@@ -11,6 +11,7 @@ package org.w3c.dom.events
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.parsing.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.kt
index bbc06b1c36e..7e42b61faeb 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.kt
@@ -11,6 +11,7 @@ package org.w3c.dom
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
 import org.w3c.dom.parsing.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.parsing.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.parsing.kt
index 1292991eac4..fa7de098789 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.parsing.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.parsing.kt
@@ -11,6 +11,7 @@ package org.w3c.dom.parsing
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.pointerevents.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.pointerevents.kt
index 0bab04de6b2..c7a38f69dfb 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.pointerevents.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.pointerevents.kt
@@ -11,6 +11,7 @@ package org.w3c.dom.pointerevents
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.svg.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.svg.kt
index ee81f1de685..565cd709eb0 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.svg.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.svg.kt
@@ -11,6 +11,7 @@ package org.w3c.dom.svg
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.url.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.url.kt
index 865e341a054..63bd88baf2c 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.dom.url.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.dom.url.kt
@@ -11,6 +11,7 @@ package org.w3c.dom.url
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.fetch.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.fetch.kt
index c4bbb5871b5..6eb72ee188e 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.fetch.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.fetch.kt
@@ -11,6 +11,7 @@ package org.w3c.fetch
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.files.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.files.kt
index 22ee1a0e015..48988fbaa2e 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.files.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.files.kt
@@ -11,6 +11,7 @@ package org.w3c.files
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.notifications.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.notifications.kt
index a04ba6e4a7e..eb3a92cf17b 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.notifications.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.notifications.kt
@@ -11,6 +11,7 @@ package org.w3c.notifications
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.performance.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.performance.kt
index f87a172ba78..6b2ad6f5ff1 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.performance.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.performance.kt
@@ -11,6 +11,7 @@ package org.w3c.performance
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.workers.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.workers.kt
index 7b11396a0fe..e97dec0a463 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.workers.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.workers.kt
@@ -11,6 +11,7 @@ package org.w3c.workers
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/stdlib/js/src/org.w3c/org.w3c.xhr.kt b/libraries/stdlib/js/src/org.w3c/org.w3c.xhr.kt
index 7602cb6cc7a..a8b76ee5672 100644
--- a/libraries/stdlib/js/src/org.w3c/org.w3c.xhr.kt
+++ b/libraries/stdlib/js/src/org.w3c/org.w3c.xhr.kt
@@ -11,6 +11,7 @@ package org.w3c.xhr
 
 import kotlin.js.*
 import org.khronos.webgl.*
+import org.w3c.css.masking.*
 import org.w3c.dom.*
 import org.w3c.dom.css.*
 import org.w3c.dom.events.*
diff --git a/libraries/tools/idl2k/build.gradle b/libraries/tools/idl2k/build.gradle
index 0aa153dfb90..531a885d9d3 100644
--- a/libraries/tools/idl2k/build.gradle
+++ b/libraries/tools/idl2k/build.gradle
@@ -34,7 +34,7 @@ generateGrammarSource {
 compileKotlin.dependsOn generateGrammarSource
 compileTestKotlin.dependsOn generateTestGrammarSource
 
-task downloadAllIdls(type: JavaExec) {
+task downloadIDL(type: JavaExec) {
     main = "org.jetbrains.idl2k.dl.DownloadKt"
     classpath = sourceSets.main.runtimeClasspath
 }
@@ -42,4 +42,4 @@ task downloadAllIdls(type: JavaExec) {
 task idl2k(type: JavaExec) {
     main = "org.jetbrains.idl2k.MainKt"
     classpath = sourceSets.main.runtimeClasspath
-}
+}
\ No newline at end of file
diff --git a/libraries/tools/idl2k/src/main/kotlin/config.kt b/libraries/tools/idl2k/src/main/kotlin/config.kt
index f3115143a7b..c9d79118228 100644
--- a/libraries/tools/idl2k/src/main/kotlin/config.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/config.kt
@@ -27,6 +27,8 @@ val urls = listOf(
         "http://www.w3.org/TR/pointerevents/" to "org.w3c.dom.pointerevents",
 
         "https://drafts.csswg.org/cssom/" to "org.w3c.dom.css",
+        "https://www.w3.org/TR/css-masking-1/" to "org.w3c.css.masking",
+
         "http://www.w3.org/TR/DOM-Parsing/" to "org.w3c.dom.parsing",
         "https://raw.githubusercontent.com/whatwg/url/master/url.html" to "org.w3c.dom.url",
 
diff --git a/libraries/tools/idl2k/src/main/kotlin/dl/download.kt b/libraries/tools/idl2k/src/main/kotlin/dl/download.kt
index 1bb58a690a6..9425614f67c 100644
--- a/libraries/tools/idl2k/src/main/kotlin/dl/download.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/dl/download.kt
@@ -33,7 +33,7 @@ fun main(args: Array<String>) {
         val arg = argsIterator.next()
 
         when (arg) {
-            "-package", "-pkg", "--package" -> if (argsIterator.hasNext()) packageFilter = argsIterator.next() else throw IllegalArgumentException("argument $arg requires argument")
+            "--pkg" -> if (argsIterator.hasNext()) packageFilter = argsIterator.next() else throw IllegalArgumentException("argument $arg requires argument")
             else -> throw IllegalArgumentException("Argument $arg is unknown")
         }
     }
@@ -79,23 +79,28 @@ private fun fetch(url: String): String? {
     }
 }
 
+private fun Appendable.append(element: Element) {
+    val text = element.text()
+    appendln(text)
+    if (!text.trimEnd().endsWith(";")) {
+        appendln(";")
+    }
+}
+
+
+private fun List<Element>.attachTo(out: Appendable) = map { element ->
+    if (!element.tag().preserveWhitespace()) {
+        Element(Tag.valueOf("pre"), element.baseUri()).appendChild(element)
+    } else element
+}.forEach { out.append(it) }
+
+
 private fun extractIDLText(rawContent: String, out: Appendable) {
     val soup = Jsoup.parse(rawContent)
-    fun append(it : Element) {
-        if (!it.tag().preserveWhitespace()) {
-            return append(Element(Tag.valueOf("pre"), it.baseUri()).appendChild(it))
-        }
-
-        val text = it.text()
-        out.appendln(text)
-        if (!text.trimEnd().endsWith(";")) {
-            out.appendln(";")
-        }
-    }
 
     soup.select(".dfn-panel").remove()
 
-    soup.select("pre.idl").filter {!it.hasClass("extract")}.forEach(::append)
-    soup.select("code.idl-code").forEach(::append)
-    soup.select("spec-idl").forEach(::append)
+    soup.select("pre.idl").filter {!it.hasClass("extract")}.attachTo(out)
+    soup.select("code.idl-code").attachTo(out)
+    soup.select("spec-idl").attachTo(out)
 }