diff --git a/js/core/css/webidl.css b/js/core/css/webidl.css
index 92a667feee..05e45ee19e 100644
--- a/js/core/css/webidl.css
+++ b/js/core/css/webidl.css
@@ -228,7 +228,7 @@ a.idlEnumItem {
   color: #c00;
 }
 
-.idlImplements a {
+.idlImplements a, .idlIncludes a {
   font-weight: bold;
 }
 
diff --git a/js/core/templates/webidl-contiguous/includes.html b/js/core/templates/webidl-contiguous/includes.html
new file mode 100644
index 0000000000..3b486f27d7
--- /dev/null
+++ b/js/core/templates/webidl-contiguous/includes.html
@@ -0,0 +1,2 @@
+<span class='idlIncludes'>{{extAttr obj indent
+}}{{idn indent}}<a>{{obj.target}}</a> includes <a>{{obj.includes}}</a>;</span>
\ No newline at end of file
diff --git a/js/core/templates/webidl-contiguous/interface.html b/js/core/templates/webidl-contiguous/interface.html
index 8db2f81bc5..e2600bbb21 100644
--- a/js/core/templates/webidl-contiguous/interface.html
+++ b/js/core/templates/webidl-contiguous/interface.html
@@ -1,4 +1,4 @@
 <span class='idlInterface' id='{{obj.idlId}}' data-idl data-title='{{obj.name}}'>{{extAttr obj indent
-}}{{idn indent}}{{partial}}{{callback}}interface <span class='idlInterfaceID'>{{#tryLink obj}}{{obj.name}}{{/tryLink
+}}{{idn indent}}{{partial}}{{callback}}interface {{mixin}}<span class='idlInterfaceID'>{{#tryLink obj}}{{obj.name}}{{/tryLink
 }}</span>{{#if obj.inheritance}} : <span class='idlSuperclass'><a>{{obj.inheritance}}</a></span>{{/if}} &#123;
 {{{children}}}{{idn indent}}&#125;;</span>
\ No newline at end of file
diff --git a/src/core/webidl.js b/src/core/webidl.js
index dcf4b72755..59f8e6f62c 100644
--- a/src/core/webidl.js
+++ b/src/core/webidl.js
@@ -22,6 +22,7 @@ var idlEnumItemTmpl = tmpls["enum-item.html"];
 var idlEnumTmpl = tmpls["enum.html"];
 var idlExtAttributeTmpl = tmpls["extended-attribute.html"];
 var idlFieldTmpl = tmpls["field.html"];
+var idlIncludesTmpl = tmpls["includes.html"];
 var idlImplementsTmpl = tmpls["implements.html"];
 var idlInterfaceTmpl = tmpls["interface.html"];
 var idlIterableTmpl = tmpls["iterable.html"];
@@ -514,12 +515,16 @@ function writeDefinition(obj, indent) {
   switch (obj.type) {
     case "typedef":
       return idlTypedefTmpl(opt);
+    case "includes":
+      return idlIncludesTmpl(opt);
     case "implements":
       return idlImplementsTmpl(opt);
     case "interface":
       return writeInterfaceDefinition(opt);
+    case "interface mixin":
+      return writeInterfaceDefinition(opt, { mixin: true });
     case "callback interface":
-      return writeInterfaceDefinition(opt, "callback ");
+      return writeInterfaceDefinition(opt, { callback: true });
     case "dictionary":
       var maxQualifiers = 0,
         maxType = 0;
@@ -643,20 +648,20 @@ function writeDefinition(obj, indent) {
   }
 }
 
-function writeInterfaceDefinition(opt, callback) {
+function writeInterfaceDefinition(opt, fixes = {}) {
   var obj = opt.obj,
     indent = opt.indent;
   var maxAttr = 0,
     maxAttrQualifiers = 0,
     maxMeth = 0,
     maxConst = 0;
-  obj.members.forEach(function(it) {
+  for (const it of obj.members) {
     if (
       typeIsWhitespace(it.type) ||
       it.type === "maplike" ||
       it.type === "iterable"
     ) {
-      return;
+      continue;
     }
     var len = idlType2Text(it.idlType).length;
     if (it.type === "attribute") {
@@ -666,7 +671,7 @@ function writeInterfaceDefinition(opt, callback) {
         qualifiersLen > maxAttrQualifiers ? qualifiersLen : maxAttrQualifiers;
     } else if (it.type === "operation") maxMeth = len > maxMeth ? len : maxMeth;
     else if (it.type === "const") maxConst = len > maxConst ? len : maxConst;
-  });
+  }
   var children = obj.members
     .map(function(ch) {
       switch (ch.type) {
@@ -692,11 +697,12 @@ function writeInterfaceDefinition(opt, callback) {
     })
     .join("");
   return idlInterfaceTmpl({
-    obj: obj,
-    indent: indent,
+    obj,
+    indent,
     partial: obj.partial ? "partial " : "",
-    callback: callback,
-    children: children,
+    callback: fixes.callback ? "callback " : "",
+    mixin: fixes.mixin ? "mixin ": "",
+    children,
   });
 }
 
@@ -867,6 +873,7 @@ function linkDefinitions(parse, definitionMap, parent, idlElem) {
     .filter(
       ({ type }) =>
         [
+          "includes",
           "implements",
           "ws",
           "ws-pea",
@@ -881,8 +888,8 @@ function linkDefinitions(parse, definitionMap, parent, idlElem) {
         // Top-level entities with linkable members.
         case "callback interface":
         case "dictionary":
-        case "exception":
         case "interface":
+        case "interface mixin":
           var partialIdx = "";
           if (defn.partial) {
             if (!idlPartials[defn.name]) {
diff --git a/tests/spec/core/webidl-spec.js b/tests/spec/core/webidl-spec.js
index 56bf6be69d..e184440579 100644
--- a/tests/spec/core/webidl-spec.js
+++ b/tests/spec/core/webidl-spec.js
@@ -143,6 +143,14 @@ describe("Core - WebIDL", function() {
     text = "callback interface SuperStar {\n};";
     expect($target.text()).toEqual(text);
 
+    $target = $("#if-mixin", doc);
+    text = "interface mixin SuperStar {\n};";
+    expect($target.text()).toEqual(text);
+
+    $target = $("#if-partial-mixin", doc);
+    text = "partial interface mixin SuperStar {\n};";
+    expect($target.text()).toEqual(text);
+
     $target = $("#if-doc", doc);
     expect(
       $target.find(":contains('DocInterface')").filter("a").attr("href")
@@ -579,7 +587,18 @@ describe("Core - WebIDL", function() {
     done();
   });
 
-  it("should handle implements", function(done) {
+  it("should handle includes", () => {
+    var $target = $("#incl-basic", doc);
+    var text = "Window includes Breakable;";
+    expect($target.text()).toEqual(text);
+    expect($target.find(".idlIncludes").length).toEqual(1);
+
+    $target = $("#incl-less-basic", doc);
+    text = "[Something]\n" + text;
+    expect($target.text()).toEqual(text);
+  });
+
+  it("should handle implements", () => {
     var $target = $("#impl-basic", doc);
     var text = "Window implements Breakable;";
     expect($target.text()).toEqual(text);
@@ -588,7 +607,6 @@ describe("Core - WebIDL", function() {
     $target = $("#impl-less-basic", doc);
     text = "[Something]\n" + text;
     expect($target.text()).toEqual(text);
-    done();
   });
 
   it("should link documentation", function() {
diff --git a/tests/spec/core/webidl.html b/tests/spec/core/webidl.html
index 22daf3daff..52ce187e1e 100644
--- a/tests/spec/core/webidl.html
+++ b/tests/spec/core/webidl.html
@@ -189,6 +189,15 @@ <h2>Interfaces</h2>
       <pre id='if-callback' class='idl'>
         callback interface SuperStar {};
       </pre>
+      <p>
+        Interface mixin .
+      </p>
+      <pre id='if-mixin' class='idl'>
+        interface mixin SuperStar {};
+      </pre>
+      <pre id='if-partial-mixin' class='idl'>
+        partial interface mixin SuperStar {};
+      </pre>
       <pre id='if-doc' class='idl'>
         interface DocInterface {};
         interface DocIsNotCaseSensitive {};
@@ -505,6 +514,21 @@ <h2>Implements</h2>
         [Something]Window implements Breakable;
       </pre>
     </section>
+    <section>
+      <h2>Includes</h2>
+      <p>
+        Basic includes.
+      </p>
+      <pre id='incl-basic' class='idl'>
+        Window includes Breakable;
+      </pre>
+      <p>
+        Less basic includes.
+      </p>
+      <pre id='incl-less-basic' class='idl'>
+        [Something]Window includes Breakable;
+      </pre>
+    </section>
     <section id="documentation">
       <h2>Documentation</h2>
       <pre id='doc-iface' class='idl'>