diff -r 000000000000 -r 959103a6100f src/share/classes/com/sun/tools/doclint/Checker.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/classes/com/sun/tools/doclint/Checker.java	Wed Apr 27 01:34:52 2016 +0800
@@ -0,0 +1,971 @@
+/*
+ * Copyright (c) 2012, 2013, 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 com.sun.tools.doclint;
+
+import java.io.IOException;
+import java.io.StringWriter;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.util.Deque;
+import java.util.EnumSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import javax.lang.model.element.Element;
+import javax.lang.model.element.ElementKind;
+import javax.lang.model.element.ExecutableElement;
+import javax.lang.model.element.Name;
+import javax.lang.model.element.VariableElement;
+import javax.lang.model.type.TypeKind;
+import javax.lang.model.type.TypeMirror;
+import javax.tools.Diagnostic.Kind;
+import javax.tools.JavaFileObject;
+
+import com.sun.source.doctree.AttributeTree;
+import com.sun.source.doctree.AuthorTree;
+import com.sun.source.doctree.DocCommentTree;
+import com.sun.source.doctree.DocRootTree;
+import com.sun.source.doctree.DocTree;
+import com.sun.source.doctree.EndElementTree;
+import com.sun.source.doctree.EntityTree;
+import com.sun.source.doctree.ErroneousTree;
+import com.sun.source.doctree.IdentifierTree;
+import com.sun.source.doctree.InheritDocTree;
+import com.sun.source.doctree.LinkTree;
+import com.sun.source.doctree.LiteralTree;
+import com.sun.source.doctree.ParamTree;
+import com.sun.source.doctree.ReferenceTree;
+import com.sun.source.doctree.ReturnTree;
+import com.sun.source.doctree.SerialDataTree;
+import com.sun.source.doctree.SerialFieldTree;
+import com.sun.source.doctree.SinceTree;
+import com.sun.source.doctree.StartElementTree;
+import com.sun.source.doctree.TextTree;
+import com.sun.source.doctree.ThrowsTree;
+import com.sun.source.doctree.UnknownBlockTagTree;
+import com.sun.source.doctree.UnknownInlineTagTree;
+import com.sun.source.doctree.ValueTree;
+import com.sun.source.doctree.VersionTree;
+import com.sun.source.util.DocTreePath;
+import com.sun.source.util.DocTreePathScanner;
+import com.sun.source.util.TreePath;
+import com.sun.tools.doclint.HtmlTag.AttrKind;
+import com.sun.tools.javac.tree.DocPretty;
+import com.sun.tools.javac.util.StringUtils;
+import static com.sun.tools.doclint.Messages.Group.*;
+
+
+/**
+ * Validate a doc comment.
+ *
+ * <p><b>This is NOT part of any supported API.
+ * If you write code that depends on this, you do so at your own
+ * risk.  This code and its internal interfaces are subject to change
+ * or deletion without notice.</b></p>
+ */
+public class Checker extends DocTreePathScanner<Void, Void> {
+    final Env env;
+
+    Set<Element> foundParams = new HashSet<>();
+    Set<TypeMirror> foundThrows = new HashSet<>();
+    Map<Element, Set<String>> foundAnchors = new HashMap<>();
+    boolean foundInheritDoc = false;
+    boolean foundReturn = false;
+
+    public enum Flag {
+        TABLE_HAS_CAPTION,
+        HAS_ELEMENT,
+        HAS_INLINE_TAG,
+        HAS_TEXT,
+        REPORTED_BAD_INLINE
+    }
+
+    static class TagStackItem {
+        final DocTree tree; // typically, but not always, StartElementTree
+        final HtmlTag tag;
+        final Set<HtmlTag.Attr> attrs;
+        final Set<Flag> flags;
+        TagStackItem(DocTree tree, HtmlTag tag) {
+            this.tree = tree;
+            this.tag = tag;
+            attrs = EnumSet.noneOf(HtmlTag.Attr.class);
+            flags = EnumSet.noneOf(Flag.class);
+        }
+        @Override
+        public String toString() {
+            return String.valueOf(tag);
+        }
+    }
+
+    private Deque<TagStackItem> tagStack; // TODO: maybe want to record starting tree as well
+    private HtmlTag currHeaderTag;
+
+    private final int implicitHeaderLevel;
+
+    // <editor-fold defaultstate="collapsed" desc="Top level">
+
+    Checker(Env env) {
+        env.getClass();
+        this.env = env;
+        tagStack = new LinkedList<>();
+        implicitHeaderLevel = env.implicitHeaderLevel;
+    }
+
+    public Void scan(DocCommentTree tree, TreePath p) {
+        env.setCurrent(p, tree);
+
+        boolean isOverridingMethod = !env.currOverriddenMethods.isEmpty();
+
+        if (p.getLeaf() == p.getCompilationUnit()) {
+            // If p points to a compilation unit, the implied declaration is the
+            // package declaration (if any) for the compilation unit.
+            // Handle this case specially, because doc comments are only
+            // expected in package-info files.
+            JavaFileObject fo = p.getCompilationUnit().getSourceFile();
+            boolean isPkgInfo = fo.isNameCompatible("package-info", JavaFileObject.Kind.SOURCE);
+            if (tree == null) {
+                if (isPkgInfo)
+                    reportMissing("dc.missing.comment");
+                return null;
+            } else {
+                if (!isPkgInfo)
+                    reportReference("dc.unexpected.comment");
+            }
+        } else {
+            if (tree == null) {
+                if (!isSynthetic() && !isOverridingMethod)
+                    reportMissing("dc.missing.comment");
+                return null;
+            }
+        }
+
+        tagStack.clear();
+        currHeaderTag = null;
+
+        foundParams.clear();
+        foundThrows.clear();
+        foundInheritDoc = false;
+        foundReturn = false;
+
+        scan(new DocTreePath(p, tree), null);
+
+        if (!isOverridingMethod) {
+            switch (env.currElement.getKind()) {
+                case METHOD:
+                case CONSTRUCTOR: {
+                    ExecutableElement ee = (ExecutableElement) env.currElement;
+                    checkParamsDocumented(ee.getTypeParameters());
+                    checkParamsDocumented(ee.getParameters());
+                    switch (ee.getReturnType().getKind()) {
+                        case VOID:
+                        case NONE:
+                            break;
+                        default:
+                            if (!foundReturn
+                                    && !foundInheritDoc
+                                    && !env.types.isSameType(ee.getReturnType(), env.java_lang_Void)) {
+                                reportMissing("dc.missing.return");
+                            }
+                    }
+                    checkThrowsDocumented(ee.getThrownTypes());
+                }
+            }
+        }
+
+        return null;
+    }
+
+    private void reportMissing(String code, Object... args) {
+        env.messages.report(MISSING, Kind.WARNING, env.currPath.getLeaf(), code, args);
+    }
+
+    private void reportReference(String code, Object... args) {
+        env.messages.report(REFERENCE, Kind.WARNING, env.currPath.getLeaf(), code, args);
+    }
+
+    @Override
+    public Void visitDocComment(DocCommentTree tree, Void ignore) {
+        super.visitDocComment(tree, ignore);
+        for (TagStackItem tsi: tagStack) {
+            warnIfEmpty(tsi, null);
+            if (tsi.tree.getKind() == DocTree.Kind.START_ELEMENT
+                    && tsi.tag.endKind == HtmlTag.EndKind.REQUIRED) {
+                StartElementTree t = (StartElementTree) tsi.tree;
+                env.messages.error(HTML, t, "dc.tag.not.closed", t.getName());
+            }
+        }
+        return null;
+    }
+    // </editor-fold>
+
+    // <editor-fold defaultstate="collapsed" desc="Text and entities.">
+
+    @Override
+    public Void visitText(TextTree tree, Void ignore) {
+        if (hasNonWhitespace(tree)) {
+            checkAllowsText(tree);
+            markEnclosingTag(Flag.HAS_TEXT);
+        }
+        return null;
+    }
+
+    @Override
+    public Void visitEntity(EntityTree tree, Void ignore) {
+        checkAllowsText(tree);
+        markEnclosingTag(Flag.HAS_TEXT);
+        String name = tree.getName().toString();
+        if (name.startsWith("#")) {
+            int v = StringUtils.toLowerCase(name).startsWith("#x")
+                    ? Integer.parseInt(name.substring(2), 16)
+                    : Integer.parseInt(name.substring(1), 10);
+            if (!Entity.isValid(v)) {
+                env.messages.error(HTML, tree, "dc.entity.invalid", name);
+            }
+        } else if (!Entity.isValid(name)) {
+            env.messages.error(HTML, tree, "dc.entity.invalid", name);
+        }
+        return null;
+    }
+
+    void checkAllowsText(DocTree tree) {
+        TagStackItem top = tagStack.peek();
+        if (top != null
+                && top.tree.getKind() == DocTree.Kind.START_ELEMENT
+                && !top.tag.acceptsText()) {
+            if (top.flags.add(Flag.REPORTED_BAD_INLINE)) {
+                env.messages.error(HTML, tree, "dc.text.not.allowed",
+                        ((StartElementTree) top.tree).getName());
+            }
+        }
+    }
+
+    // </editor-fold>
+
+    // <editor-fold defaultstate="collapsed" desc="HTML elements">
+
+    @Override
+    public Void visitStartElement(StartElementTree tree, Void ignore) {
+        final Name treeName = tree.getName();
+        final HtmlTag t = HtmlTag.get(treeName);
+        if (t == null) {
+            env.messages.error(HTML, tree, "dc.tag.unknown", treeName);
+        } else {
+            boolean done = false;
+            for (TagStackItem tsi: tagStack) {
+                if (tsi.tag.accepts(t)) {
+                    while (tagStack.peek() != tsi) {
+                        warnIfEmpty(tagStack.peek(), null);
+                        tagStack.pop();
+                    }
+                    done = true;
+                    break;
+                } else if (tsi.tag.endKind != HtmlTag.EndKind.OPTIONAL) {
+                    done = true;
+                    break;
+                }
+            }
+            if (!done && HtmlTag.BODY.accepts(t)) {
+                while (!tagStack.isEmpty()) {
+                    warnIfEmpty(tagStack.peek(), null);
+                    tagStack.pop();
+                }
+            }
+
+            markEnclosingTag(Flag.HAS_ELEMENT);
+            checkStructure(tree, t);
+
+            // tag specific checks
+            switch (t) {
+                // check for out of sequence headers, such as <h1>...</h1>  <h3>...</h3>
+                case H1: case H2: case H3: case H4: case H5: case H6:
+                    checkHeader(tree, t);
+                    break;
+            }
+
+            if (t.flags.contains(HtmlTag.Flag.NO_NEST)) {
+                for (TagStackItem i: tagStack) {
+                    if (t == i.tag) {
+                        env.messages.warning(HTML, tree, "dc.tag.nested.not.allowed", treeName);
+                        break;
+                    }
+                }
+            }
+        }
+
+        // check for self closing tags, such as <a id="name"/>
+        if (tree.isSelfClosing()) {
+            env.messages.error(HTML, tree, "dc.tag.self.closing", treeName);
+        }
+
+        try {
+            TagStackItem parent = tagStack.peek();
+            TagStackItem top = new TagStackItem(tree, t);
+            tagStack.push(top);
+
+            super.visitStartElement(tree, ignore);
+
+            // handle attributes that may or may not have been found in start element
+            if (t != null) {
+                switch (t) {
+                    case CAPTION:
+                        if (parent != null && parent.tag == HtmlTag.TABLE)
+                            parent.flags.add(Flag.TABLE_HAS_CAPTION);
+                        break;
+
+                    case IMG:
+                        if (!top.attrs.contains(HtmlTag.Attr.ALT))
+                            env.messages.error(ACCESSIBILITY, tree, "dc.no.alt.attr.for.image");
+                        break;
+                }
+            }
+
+            return null;
+        } finally {
+
+            if (t == null || t.endKind == HtmlTag.EndKind.NONE)
+                tagStack.pop();
+        }
+    }
+
+    private void checkStructure(StartElementTree tree, HtmlTag t) {
+        Name treeName = tree.getName();
+        TagStackItem top = tagStack.peek();
+        switch (t.blockType) {
+            case BLOCK:
+                if (top == null || top.tag.accepts(t))
+                    return;
+
+                switch (top.tree.getKind()) {
+                    case START_ELEMENT: {
+                        if (top.tag.blockType == HtmlTag.BlockType.INLINE) {
+                            Name name = ((StartElementTree) top.tree).getName();
+                            env.messages.error(HTML, tree, "dc.tag.not.allowed.inline.element",
+                                    treeName, name);
+                            return;
+                        }
+                    }
+                    break;
+
+                    case LINK:
+                    case LINK_PLAIN: {
+                        String name = top.tree.getKind().tagName;
+                        env.messages.error(HTML, tree, "dc.tag.not.allowed.inline.tag",
+                                treeName, name);
+                        return;
+                    }
+                }
+                break;
+
+            case INLINE:
+                if (top == null || top.tag.accepts(t))
+                    return;
+                break;
+
+            case LIST_ITEM:
+            case TABLE_ITEM:
+                if (top != null) {
+                    // reset this flag so subsequent bad inline content gets reported
+                    top.flags.remove(Flag.REPORTED_BAD_INLINE);
+                    if (top.tag.accepts(t))
+                        return;
+                }
+                break;
+
+            case OTHER:
+                env.messages.error(HTML, tree, "dc.tag.not.allowed", treeName);
+                return;
+        }
+
+        env.messages.error(HTML, tree, "dc.tag.not.allowed.here", treeName);
+    }
+
+    private void checkHeader(StartElementTree tree, HtmlTag tag) {
+        // verify the new tag
+        if (getHeaderLevel(tag) > getHeaderLevel(currHeaderTag) + 1) {
+            if (currHeaderTag == null) {
+                env.messages.error(ACCESSIBILITY, tree, "dc.tag.header.sequence.1", tag);
+            } else {
+                env.messages.error(ACCESSIBILITY, tree, "dc.tag.header.sequence.2",
+                    tag, currHeaderTag);
+            }
+        }
+
+        currHeaderTag = tag;
+    }
+
+    private int getHeaderLevel(HtmlTag tag) {
+        if (tag == null)
+            return implicitHeaderLevel;
+        switch (tag) {
+            case H1: return 1;
+            case H2: return 2;
+            case H3: return 3;
+            case H4: return 4;
+            case H5: return 5;
+            case H6: return 6;
+            default: throw new IllegalArgumentException();
+        }
+    }
+
+    @Override
+    public Void visitEndElement(EndElementTree tree, Void ignore) {
+        final Name treeName = tree.getName();
+        final HtmlTag t = HtmlTag.get(treeName);
+        if (t == null) {
+            env.messages.error(HTML, tree, "dc.tag.unknown", treeName);
+        } else if (t.endKind == HtmlTag.EndKind.NONE) {
+            env.messages.error(HTML, tree, "dc.tag.end.not.permitted", treeName);
+        } else {
+            boolean done = false;
+            while (!tagStack.isEmpty()) {
+                TagStackItem top = tagStack.peek();
+                if (t == top.tag) {
+                    switch (t) {
+                        case TABLE:
+                            if (!top.attrs.contains(HtmlTag.Attr.SUMMARY)
+                                    && !top.flags.contains(Flag.TABLE_HAS_CAPTION)) {
+                                env.messages.error(ACCESSIBILITY, tree,
+                                        "dc.no.summary.or.caption.for.table");
+                            }
+                    }
+                    warnIfEmpty(top, tree);
+                    tagStack.pop();
+                    done = true;
+                    break;
+                } else if (top.tag == null || top.tag.endKind != HtmlTag.EndKind.REQUIRED) {
+                    tagStack.pop();
+                } else {
+                    boolean found = false;
+                    for (TagStackItem si: tagStack) {
+                        if (si.tag == t) {
+                            found = true;
+                            break;
+                        }
+                    }
+                    if (found && top.tree.getKind() == DocTree.Kind.START_ELEMENT) {
+                        env.messages.error(HTML, top.tree, "dc.tag.start.unmatched",
+                                ((StartElementTree) top.tree).getName());
+                        tagStack.pop();
+                    } else {
+                        env.messages.error(HTML, tree, "dc.tag.end.unexpected", treeName);
+                        done = true;
+                        break;
+                    }
+                }
+            }
+
+            if (!done && tagStack.isEmpty()) {
+                env.messages.error(HTML, tree, "dc.tag.end.unexpected", treeName);
+            }
+        }
+
+        return super.visitEndElement(tree, ignore);
+    }
+
+    void warnIfEmpty(TagStackItem tsi, DocTree endTree) {
+        if (tsi.tag != null && tsi.tree instanceof StartElementTree) {
+            if (tsi.tag.flags.contains(HtmlTag.Flag.EXPECT_CONTENT)
+                    && !tsi.flags.contains(Flag.HAS_TEXT)
+                    && !tsi.flags.contains(Flag.HAS_ELEMENT)
+                    && !tsi.flags.contains(Flag.HAS_INLINE_TAG)) {
+                DocTree tree = (endTree != null) ? endTree : tsi.tree;
+                Name treeName = ((StartElementTree) tsi.tree).getName();
+                env.messages.warning(HTML, tree, "dc.tag.empty", treeName);
+            }
+        }
+    }
+
+    // </editor-fold>
+
+    // <editor-fold defaultstate="collapsed" desc="HTML attributes">
+
+    @Override @SuppressWarnings("fallthrough")
+    public Void visitAttribute(AttributeTree tree, Void ignore) {
+        HtmlTag currTag = tagStack.peek().tag;
+        if (currTag != null) {
+            Name name = tree.getName();
+            HtmlTag.Attr attr = currTag.getAttr(name);
+            if (attr != null) {
+                boolean first = tagStack.peek().attrs.add(attr);
+                if (!first)
+                    env.messages.error(HTML, tree, "dc.attr.repeated", name);
+            }
+            AttrKind k = currTag.getAttrKind(name);
+            switch (k) {
+                case OK:
+                    break;
+
+                case INVALID:
+                    env.messages.error(HTML, tree, "dc.attr.unknown", name);
+                    break;
+
+                case OBSOLETE:
+                    env.messages.warning(ACCESSIBILITY, tree, "dc.attr.obsolete", name);
+                    break;
+
+                case USE_CSS:
+                    env.messages.warning(ACCESSIBILITY, tree, "dc.attr.obsolete.use.css", name);
+                    break;
+            }
+
+            if (attr != null) {
+                switch (attr) {
+                    case NAME:
+                        if (currTag != HtmlTag.A) {
+                            break;
+                        }
+                        // fallthrough
+                    case ID:
+                        String value = getAttrValue(tree);
+                        if (value == null) {
+                            env.messages.error(HTML, tree, "dc.anchor.value.missing");
+                        } else {
+                            if (!validName.matcher(value).matches()) {
+                                env.messages.error(HTML, tree, "dc.invalid.anchor", value);
+                            }
+                            if (!checkAnchor(value)) {
+                                env.messages.error(HTML, tree, "dc.anchor.already.defined", value);
+                            }
+                        }
+                        break;
+
+                    case HREF:
+                        if (currTag == HtmlTag.A) {
+                            String v = getAttrValue(tree);
+                            if (v == null || v.isEmpty()) {
+                                env.messages.error(HTML, tree, "dc.attr.lacks.value");
+                            } else {
+                                Matcher m = docRoot.matcher(v);
+                                if (m.matches()) {
+                                    String rest = m.group(2);
+                                    if (!rest.isEmpty())
+                                        checkURI(tree, rest);
+                                } else {
+                                    checkURI(tree, v);
+                                }
+                            }
+                        }
+                        break;
+
+                    case VALUE:
+                        if (currTag == HtmlTag.LI) {
+                            String v = getAttrValue(tree);
+                            if (v == null || v.isEmpty()) {
+                                env.messages.error(HTML, tree, "dc.attr.lacks.value");
+                            } else if (!validNumber.matcher(v).matches()) {
+                                env.messages.error(HTML, tree, "dc.attr.not.number");
+                            }
+                        }
+                        break;
+                }
+            }
+        }
+
+        // TODO: basic check on value
+
+        return super.visitAttribute(tree, ignore);
+    }
+
+    private boolean checkAnchor(String name) {
+        Element e = getEnclosingPackageOrClass(env.currElement);
+        if (e == null)
+            return true;
+        Set<String> set = foundAnchors.get(e);
+        if (set == null)
+            foundAnchors.put(e, set = new HashSet<>());
+        return set.add(name);
+    }
+
+    private Element getEnclosingPackageOrClass(Element e) {
+        while (e != null) {
+            switch (e.getKind()) {
+                case CLASS:
+                case ENUM:
+                case INTERFACE:
+                case PACKAGE:
+                    return e;
+                default:
+                    e = e.getEnclosingElement();
+            }
+        }
+        return e;
+    }
+
+    // http://www.w3.org/TR/html401/types.html#type-name
+    private static final Pattern validName = Pattern.compile("[A-Za-z][A-Za-z0-9-_:.]*");
+
+    private static final Pattern validNumber = Pattern.compile("-?[0-9]+");
+
+    // pattern to remove leading {@docRoot}/?
+    private static final Pattern docRoot = Pattern.compile("(?i)(\\{@docRoot *\\}/?)?(.*)");
+
+    private String getAttrValue(AttributeTree tree) {
+        if (tree.getValue() == null)
+            return null;
+
+        StringWriter sw = new StringWriter();
+        try {
+            new DocPretty(sw).print(tree.getValue());
+        } catch (IOException e) {
+            // cannot happen
+        }
+        // ignore potential use of entities for now
+        return sw.toString();
+    }
+
+    private void checkURI(AttributeTree tree, String uri) {
+        try {
+            URI u = new URI(uri);
+        } catch (URISyntaxException e) {
+            env.messages.error(HTML, tree, "dc.invalid.uri", uri);
+        }
+    }
+    // </editor-fold>
+
+    // <editor-fold defaultstate="collapsed" desc="javadoc tags">
+
+    @Override
+    public Void visitAuthor(AuthorTree tree, Void ignore) {
+        warnIfEmpty(tree, tree.getName());
+        return super.visitAuthor(tree, ignore);
+    }
+
+    @Override
+    public Void visitDocRoot(DocRootTree tree, Void ignore) {
+        markEnclosingTag(Flag.HAS_INLINE_TAG);
+        return super.visitDocRoot(tree, ignore);
+    }
+
+    @Override
+    public Void visitInheritDoc(InheritDocTree tree, Void ignore) {
+        markEnclosingTag(Flag.HAS_INLINE_TAG);
+        // TODO: verify on overridden method
+        foundInheritDoc = true;
+        return super.visitInheritDoc(tree, ignore);
+    }
+
+    @Override
+    public Void visitLink(LinkTree tree, Void ignore) {
+        markEnclosingTag(Flag.HAS_INLINE_TAG);
+        // simulate inline context on tag stack
+        HtmlTag t = (tree.getKind() == DocTree.Kind.LINK)
+                ? HtmlTag.CODE : HtmlTag.SPAN;
+        tagStack.push(new TagStackItem(tree, t));
+        try {
+            return super.visitLink(tree, ignore);
+        } finally {
+            tagStack.pop();
+        }
+    }
+
+    @Override
+    public Void visitLiteral(LiteralTree tree, Void ignore) {
+        markEnclosingTag(Flag.HAS_INLINE_TAG);
+        if (tree.getKind() == DocTree.Kind.CODE) {
+            for (TagStackItem tsi: tagStack) {
+                if (tsi.tag == HtmlTag.CODE) {
+                    env.messages.warning(HTML, tree, "dc.tag.code.within.code");
+                    break;
+                }
+            }
+        }
+        return super.visitLiteral(tree, ignore);
+    }
+
+    @Override
+    @SuppressWarnings("fallthrough")
+    public Void visitParam(ParamTree tree, Void ignore) {
+        boolean typaram = tree.isTypeParameter();
+        IdentifierTree nameTree = tree.getName();
+        Element paramElement = nameTree != null ? env.trees.getElement(new DocTreePath(getCurrentPath(), nameTree)) : null;
+
+        if (paramElement == null) {
+            switch (env.currElement.getKind()) {
+                case CLASS: case INTERFACE: {
+                    if (!typaram) {
+                        env.messages.error(REFERENCE, tree, "dc.invalid.param");
+                        break;
+                    }
+                }
+                case METHOD: case CONSTRUCTOR: {
+                    env.messages.error(REFERENCE, nameTree, "dc.param.name.not.found");
+                    break;
+                }
+
+                default:
+                    env.messages.error(REFERENCE, tree, "dc.invalid.param");
+                    break;
+            }
+        } else {
+            foundParams.add(paramElement);
+        }
+
+        warnIfEmpty(tree, tree.getDescription());
+        return super.visitParam(tree, ignore);
+    }
+
+    private void checkParamsDocumented(List<? extends Element> list) {
+        if (foundInheritDoc)
+            return;
+
+        for (Element e: list) {
+            if (!foundParams.contains(e)) {
+                CharSequence paramName = (e.getKind() == ElementKind.TYPE_PARAMETER)
+                        ? "<" + e.getSimpleName() + ">"
+                        : e.getSimpleName();
+                reportMissing("dc.missing.param", paramName);
+            }
+        }
+    }
+
+    @Override
+    public Void visitReference(ReferenceTree tree, Void ignore) {
+        String sig = tree.getSignature();
+        if (sig.contains("<") || sig.contains(">"))
+            env.messages.error(REFERENCE, tree, "dc.type.arg.not.allowed");
+
+        Element e = env.trees.getElement(getCurrentPath());
+        if (e == null)
+            env.messages.error(REFERENCE, tree, "dc.ref.not.found");
+        return super.visitReference(tree, ignore);
+    }
+
+    @Override
+    public Void visitReturn(ReturnTree tree, Void ignore) {
+        Element e = env.trees.getElement(env.currPath);
+        if (e.getKind() != ElementKind.METHOD
+                || ((ExecutableElement) e).getReturnType().getKind() == TypeKind.VOID)
+            env.messages.error(REFERENCE, tree, "dc.invalid.return");
+        foundReturn = true;
+        warnIfEmpty(tree, tree.getDescription());
+        return super.visitReturn(tree, ignore);
+    }
+
+    @Override
+    public Void visitSerialData(SerialDataTree tree, Void ignore) {
+        warnIfEmpty(tree, tree.getDescription());
+        return super.visitSerialData(tree, ignore);
+    }
+
+    @Override
+    public Void visitSerialField(SerialFieldTree tree, Void ignore) {
+        warnIfEmpty(tree, tree.getDescription());
+        return super.visitSerialField(tree, ignore);
+    }
+
+    @Override
+    public Void visitSince(SinceTree tree, Void ignore) {
+        warnIfEmpty(tree, tree.getBody());
+        return super.visitSince(tree, ignore);
+    }
+
+    @Override
+    public Void visitThrows(ThrowsTree tree, Void ignore) {
+        ReferenceTree exName = tree.getExceptionName();
+        Element ex = env.trees.getElement(new DocTreePath(getCurrentPath(), exName));
+        if (ex == null) {
+            env.messages.error(REFERENCE, tree, "dc.ref.not.found");
+        } else if (isThrowable(ex.asType())) {
+            switch (env.currElement.getKind()) {
+                case CONSTRUCTOR:
+                case METHOD:
+                    if (isCheckedException(ex.asType())) {
+                        ExecutableElement ee = (ExecutableElement) env.currElement;
+                        checkThrowsDeclared(exName, ex.asType(), ee.getThrownTypes());
+                    }
+                    break;
+                default:
+                    env.messages.error(REFERENCE, tree, "dc.invalid.throws");
+            }
+        } else {
+            env.messages.error(REFERENCE, tree, "dc.invalid.throws");
+        }
+        warnIfEmpty(tree, tree.getDescription());
+        return scan(tree.getDescription(), ignore);
+    }
+
+    private boolean isThrowable(TypeMirror tm) {
+        switch (tm.getKind()) {
+            case DECLARED:
+            case TYPEVAR:
+                return env.types.isAssignable(tm, env.java_lang_Throwable);
+        }
+        return false;
+    }
+
+    private void checkThrowsDeclared(ReferenceTree tree, TypeMirror t, List<? extends TypeMirror> list) {
+        boolean found = false;
+        for (TypeMirror tl : list) {
+            if (env.types.isAssignable(t, tl)) {
+                foundThrows.add(tl);
+                found = true;
+            }
+        }
+        if (!found)
+            env.messages.error(REFERENCE, tree, "dc.exception.not.thrown", t);
+    }
+
+    private void checkThrowsDocumented(List<? extends TypeMirror> list) {
+        if (foundInheritDoc)
+            return;
+
+        for (TypeMirror tl: list) {
+            if (isCheckedException(tl) && !foundThrows.contains(tl))
+                reportMissing("dc.missing.throws", tl);
+        }
+    }
+
+    @Override
+    public Void visitUnknownBlockTag(UnknownBlockTagTree tree, Void ignore) {
+        checkUnknownTag(tree, tree.getTagName());
+        return super.visitUnknownBlockTag(tree, ignore);
+    }
+
+    @Override
+    public Void visitUnknownInlineTag(UnknownInlineTagTree tree, Void ignore) {
+        checkUnknownTag(tree, tree.getTagName());
+        return super.visitUnknownInlineTag(tree, ignore);
+    }
+
+    private void checkUnknownTag(DocTree tree, String tagName) {
+        if (env.customTags != null && !env.customTags.contains(tagName))
+            env.messages.error(SYNTAX, tree, "dc.tag.unknown", tagName);
+    }
+
+    @Override
+    public Void visitValue(ValueTree tree, Void ignore) {
+        ReferenceTree ref = tree.getReference();
+        if (ref == null || ref.getSignature().isEmpty()) {
+            if (!isConstant(env.currElement))
+                env.messages.error(REFERENCE, tree, "dc.value.not.allowed.here");
+        } else {
+            Element e = env.trees.getElement(new DocTreePath(getCurrentPath(), ref));
+            if (!isConstant(e))
+                env.messages.error(REFERENCE, tree, "dc.value.not.a.constant");
+        }
+
+        markEnclosingTag(Flag.HAS_INLINE_TAG);
+        return super.visitValue(tree, ignore);
+    }
+
+    private boolean isConstant(Element e) {
+        if (e == null)
+            return false;
+
+        switch (e.getKind()) {
+            case FIELD:
+                Object value = ((VariableElement) e).getConstantValue();
+                return (value != null); // can't distinguish "not a constant" from "constant is null"
+            default:
+                return false;
+        }
+    }
+
+    @Override
+    public Void visitVersion(VersionTree tree, Void ignore) {
+        warnIfEmpty(tree, tree.getBody());
+        return super.visitVersion(tree, ignore);
+    }
+
+    @Override
+    public Void visitErroneous(ErroneousTree tree, Void ignore) {
+        env.messages.error(SYNTAX, tree, null, tree.getDiagnostic().getMessage(null));
+        return null;
+    }
+    // </editor-fold>
+
+    // <editor-fold defaultstate="collapsed" desc="Utility methods">
+
+    private boolean isCheckedException(TypeMirror t) {
+        return !(env.types.isAssignable(t, env.java_lang_Error)
+                || env.types.isAssignable(t, env.java_lang_RuntimeException));
+    }
+
+    private boolean isSynthetic() {
+        switch (env.currElement.getKind()) {
+            case CONSTRUCTOR:
+                // A synthetic default constructor has the same pos as the
+                // enclosing class
+                TreePath p = env.currPath;
+                return env.getPos(p) == env.getPos(p.getParentPath());
+        }
+        return false;
+    }
+
+    void markEnclosingTag(Flag flag) {
+        TagStackItem top = tagStack.peek();
+        if (top != null)
+            top.flags.add(flag);
+    }
+
+    String toString(TreePath p) {
+        StringBuilder sb = new StringBuilder("TreePath[");
+        toString(p, sb);
+        sb.append("]");
+        return sb.toString();
+    }
+
+    void toString(TreePath p, StringBuilder sb) {
+        TreePath parent = p.getParentPath();
+        if (parent != null) {
+            toString(parent, sb);
+            sb.append(",");
+        }
+       sb.append(p.getLeaf().getKind()).append(":").append(env.getPos(p)).append(":S").append(env.getStartPos(p));
+    }
+
+    void warnIfEmpty(DocTree tree, List<? extends DocTree> list) {
+        for (DocTree d: list) {
+            switch (d.getKind()) {
+                case TEXT:
+                    if (hasNonWhitespace((TextTree) d))
+                        return;
+                    break;
+                default:
+                    return;
+            }
+        }
+        env.messages.warning(SYNTAX, tree, "dc.empty", tree.getKind().tagName);
+    }
+
+    boolean hasNonWhitespace(TextTree tree) {
+        String s = tree.getBody();
+        for (int i = 0; i < s.length(); i++) {
+            if (!Character.isWhitespace(s.charAt(i)))
+                return true;
+        }
+        return false;
+    }
+
+    // </editor-fold>
+
+}