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diff --git a/js/mathjax/extensions/fast-preview.js b/js/mathjax/extensions/fast-preview.js
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+// @license magnet:?xt=urn:btih:8e4f440f4c65981c5bf93c76d35135ba5064d8b7dn=apache-2.0.txt Apache-2.0
+/* -*- Mode: Javascript; indent-tabs-mode:nil; js-indent-level: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+
+/*************************************************************
+ *
+ *  MathJax/extensions/fast-preview.js
+ *  
+ *  Implements a fast preview using the PreviewHTML output jax
+ *  and then a slower update to the more accurate HTML-CSS output
+ *  (or whatever the user has selected).
+ *  
+ *  ---------------------------------------------------------------------
+ *  
+ *  Copyright (c) 2014-2020 The MathJax Consortium
+ * 
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+(function (HUB,HTML,BROWSER) {
+  
+  var SETTINGS = HUB.config.menuSettings;
+  var JAX = MathJax.OutputJax;
+  var msieColorBug = BROWSER.isMSIE && (document.documentMode||0) < 8;
+
+  var FastPreview = MathJax.Extension["fast-preview"] = {
+    version: "2.7.9",
+    enabled: true,
+
+    //
+    //  Configuration for the chunking of the main output
+    //  after the previews have been created, and other configuration.
+    //
+    config: HUB.CombineConfig("fast-preview",{
+      Chunks: {EqnChunk: 10000, EqnChunkFactor: 1, EqnChunkDelay: 0},
+      color: "inherit!important",
+      updateTime: 30, updateDelay: 6,
+      messageStyle: "none",
+      disabled: BROWSER.isMSIE && !BROWSER.versionAtLeast("8.0")
+    }),
+
+    //
+    //  Ajust the chunking of the output jax
+    //
+    Config: function () {
+      if (HUB.config["CHTML-preview"])
+        MathJax.Hub.Config({"fast-preview": HUB.config["CHTML-preview"]});
+      var update, delay, style, done, saved;
+      var config = this.config;
+
+      if (!config.disabled && SETTINGS.FastPreview == null)
+        HUB.Config({menuSettings:{FastPreview:true}});
+      if (SETTINGS.FastPreview) {
+        MathJax.Ajax.Styles({".MathJax_Preview .MJXf-math":{color:config.color}});
+        HUB.Config({"HTML-CSS": config.Chunks, CommonHTML: config.Chunks, SVG: config.Chunks});
+      }
+      HUB.Register.MessageHook("Begin Math Output",function () {
+        if (!done && FastPreview.Active()) {
+          update = HUB.processUpdateTime; delay = HUB.processUpdateDelay;
+          style = HUB.config.messageStyle;
+          HUB.processUpdateTime = config.updateTime;
+          HUB.processUpdateDelay = config.updateDelay;
+          HUB.Config({messageStyle: config.messageStyle});
+          MathJax.Message.Clear(0,0);
+          saved = true;
+        }
+      });
+      HUB.Register.MessageHook("End Math Output",function () {
+        if (!done && saved) {
+          HUB.processUpdateTime = update;
+          HUB.processUpdateDelay = delay;
+          HUB.Config({messageStyle: style});
+          done = true;
+        }
+      });
+    },
+    
+    //
+    //  Allow page to override user settings (for things like editor previews)
+    //
+    Disable: function () {this.enabled = false},
+    Enable: function () {this.enabled = true},
+    
+    Active: function () {
+      return SETTINGS.FastPreview && this.enabled &&
+             !(JAX[SETTINGS.renderer]||{}).noFastPreview;
+    },
+
+    //
+    //  Insert a preview span, if there isn't one already,
+    //  and call the PreviewHTML output jax to create the preview
+    //
+    Preview: function (data) {
+      if (!this.Active() || !data.script.parentNode) return;
+      var preview = data.script.MathJax.preview || data.script.previousSibling;
+      if (!preview || preview.className !== MathJax.Hub.config.preRemoveClass) {
+        preview = HTML.Element("span",{className:MathJax.Hub.config.preRemoveClass});
+        data.script.parentNode.insertBefore(preview,data.script);
+        data.script.MathJax.preview = preview;
+      }
+      preview.innerHTML = "";
+      preview.style.color = (msieColorBug ? "black" : "inherit");
+      return this.postFilter(preview,data);
+    },
+    postFilter: function (preview,data) {
+      //
+      //  Load the PreviewHTML jax if it is not already loaded
+      //
+      if (!data.math.root.toPreviewHTML) {
+        var queue = MathJax.Callback.Queue();
+        queue.Push(
+          ["Require",MathJax.Ajax,"[MathJax]/jax/output/PreviewHTML/config.js"],
+          ["Require",MathJax.Ajax,"[MathJax]/jax/output/PreviewHTML/jax.js"]
+        );
+        HUB.RestartAfter(queue.Push({}));
+      }
+      data.math.root.toPreviewHTML(preview);
+    },
+
+    //
+    //  Hook into the input jax postFilter to create the previews as
+    //  the input jax are processed.
+    //
+    Register: function (name) {
+      HUB.Register.StartupHook(name+" Jax Require",function () {
+        var jax = MathJax.InputJax[name];
+        jax.postfilterHooks.Add(["Preview",MathJax.Extension["fast-preview"]],50);
+      });
+    }
+  }
+
+  //
+  //  Hook into each input jax
+  //
+  FastPreview.Register("TeX");
+  FastPreview.Register("MathML");
+  FastPreview.Register("AsciiMath");
+  
+  HUB.Register.StartupHook("End Config",["Config",FastPreview]);
+  
+  HUB.Startup.signal.Post("fast-preview Ready");
+
+})(MathJax.Hub,MathJax.HTML,MathJax.Hub.Browser);
+
+MathJax.Ajax.loadComplete("[MathJax]/extensions/fast-preview.js");
+
+// @license-end