diff -r 14e098407bb0 -r ad69fd32778e make/jdk/src/classes/build/tools/taglet/Preview.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/make/jdk/src/classes/build/tools/taglet/Preview.java	Mon Oct 21 15:38:26 2019 +0200
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package build.tools.taglet;
+
+import java.util.Arrays;
+import java.util.EnumSet;
+import java.util.List;
+import java.util.Set;
+import java.util.function.Predicate;
+import javax.lang.model.element.Element;
+import com.sun.source.doctree.DocTree;
+import com.sun.source.doctree.TextTree;
+import com.sun.source.doctree.UnknownInlineTagTree;
+import jdk.javadoc.doclet.Taglet;
+import static jdk.javadoc.doclet.Taglet.Location.*;
+
+/**
+ * An block tag to insert a standard warning about a preview API.
+ */
+public class Preview implements Taglet {
+
+    /** Returns the set of locations in which a taglet may be used. */
+    @Override
+    public Set<Location> getAllowedLocations() {
+        return EnumSet.of(MODULE, PACKAGE, TYPE, CONSTRUCTOR, METHOD, FIELD);
+    }
+
+    @Override
+    public boolean isInlineTag() {
+        return true;
+    }
+
+    @Override
+    public String getName() {
+        return "preview";
+    }
+
+    @Override
+    public String toString(List<? extends DocTree> tags, Element elem) {
+        UnknownInlineTagTree previewTag = (UnknownInlineTagTree) tags.get(0);
+        List<? extends DocTree> previewContent = previewTag.getContent();
+        String previewText = ((TextTree) previewContent.get(0)).getBody();
+        String[] summaryAndDetails = previewText.split("\n\r?\n\r?");
+        String summary = summaryAndDetails[0];
+        String details = summaryAndDetails.length > 1 ? summaryAndDetails[1] : summaryAndDetails[0];
+        StackTraceElement[] stackTrace = new Exception().getStackTrace();
+        Predicate<StackTraceElement> isSummary =
+                el -> el.getClassName().endsWith("HtmlDocletWriter") &&
+                      el.getMethodName().equals("addSummaryComment");
+        if (Arrays.stream(stackTrace).anyMatch(isSummary)) {
+            return "<div style=\"display:inline-block; font-weight:bold\">" + summary + "</div><br>";
+        }
+        return "<div style=\"border: 1px solid red; border-radius: 5px; padding: 5px; display:inline-block; font-size: larger\">" + details + "</div><br>";
+    }
+}
+