Source/WebCore/editing/MarkupAccumulator.cpp

/*
 * Copyright (C) 2004-2017 Apple Inc. All rights reserved.
 * Copyright (C) 2009, 2010 Google Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include "config.h"
#include "MarkupAccumulator.h"

#include "CDATASection.h"
#include "Comment.h"
#include "DocumentFragment.h"
#include "DocumentType.h"
#include "Editor.h"
#include "ElementInlines.h"
#include "HTMLElement.h"
#include "HTMLNames.h"
#include "HTMLTemplateElement.h"
#include "ProcessingInstruction.h"
#include "XLinkNames.h"
#include "XMLNSNames.h"
#include "XMLNames.h"
#include <wtf/NeverDestroyed.h>
#include <wtf/URL.h>
#include <wtf/unicode/CharacterNames.h>

namespace WebCore {

using namespace HTMLNames;

struct EntityDescription {
    const char* characters;
    unsigned char length;
    unsigned char mask;
};

static const EntityDescription entitySubstitutionList[] = {
    { "", 0 , 0 },
    { "&amp;", 5 , EntityAmp },
    { "&lt;", 4, EntityLt },
    { "&gt;", 4, EntityGt },
    { "&quot;", 6, EntityQuot },
    { "&nbsp;", 6, EntityNbsp },
    { "&#9;", 4, EntityTab },
    { "&#10;", 5, EntityLineFeed },
    { "&#13;", 5, EntityCarriageReturn },
};

enum EntitySubstitutionIndex {
    EntitySubstitutionNullIndex = 0,
    EntitySubstitutionAmpIndex = 1,
    EntitySubstitutionLtIndex = 2,
    EntitySubstitutionGtIndex = 3,
    EntitySubstitutionQuotIndex = 4,
    EntitySubstitutionNbspIndex = 5,
    EntitySubstitutionTabIndex = 6,
    EntitySubstitutionLineFeedIndex = 7,
    EntitySubstitutionCarriageReturnIndex = 8,
};

static const unsigned maximumEscapedentityCharacter = noBreakSpace;
static const uint8_t entityMap[maximumEscapedentityCharacter + 1] = {
    0, 0, 0, 0, 0, 0, 0, 0, 0,
    EntitySubstitutionTabIndex, // '\t'.
    EntitySubstitutionLineFeedIndex, // '\n'.
    0, 0,
    EntitySubstitutionCarriageReturnIndex, // '\r'.
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    EntitySubstitutionQuotIndex, // '"'.
    0, 0, 0,
    EntitySubstitutionAmpIndex, // '&'.
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    EntitySubstitutionLtIndex, // '<'.
    0,
    EntitySubstitutionGtIndex, // '>'.
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    EntitySubstitutionNbspIndex // noBreakSpace.
};

static bool elementCannotHaveEndTag(const Node& node)
{
    if (!is<HTMLElement>(node))
        return false;

    // From https://html.spec.whatwg.org/#serialising-html-fragments:
    // If current node is an area, base, basefont, bgsound, br, col, embed, frame, hr, img,
    // input, keygen, link, meta, param, source, track or wbr element, then continue on to
    // the next child node at this point.
    static const AtomStringImpl* const localNames[] = {
        areaTag->localName().impl(),
        baseTag->localName().impl(),
        basefontTag->localName().impl(),
        bgsoundTag->localName().impl(),
        brTag->localName().impl(),
        colTag->localName().impl(),
        embedTag->localName().impl(),
        frameTag->localName().impl(),
        hrTag->localName().impl(),
        imgTag->localName().impl(),
        inputTag->localName().impl(),
        keygenTag->localName().impl(),
        linkTag->localName().impl(),
        metaTag->localName().impl(),
        paramTag->localName().impl(),
        sourceTag->localName().impl(),
        trackTag->localName().impl(),
        wbrTag->localName().impl()
    };

    auto* const elementName = downcast<HTMLElement>(node).localName().impl();
    for (auto* name : localNames) {
        if (name == elementName)
            return true;
    }

    return false;
}

// Rules of self-closure
// 1. No elements in HTML documents use the self-closing syntax.
// 2. Elements w/ children never self-close because they use a separate end tag.
// 3. HTML elements which do not have a "forbidden" end tag will close with a separate end tag.
// 4. Other elements self-close.
static bool shouldSelfClose(const Element& element, SerializationSyntax syntax)
{
    if (syntax != SerializationSyntax::XML && element.document().isHTMLDocument())
        return false;
    if (element.hasChildNodes())
        return false;
    if (element.isHTMLElement() && !elementCannotHaveEndTag(element))
        return false;
    return true;
}

template<typename CharacterType>
static inline void appendCharactersReplacingEntitiesInternal(StringBuilder& result, const String& source, unsigned offset, unsigned length, EntityMask entityMask)
{
    const CharacterType* text = source.characters<CharacterType>() + offset;

    size_t positionAfterLastEntity = 0;
    for (size_t i = 0; i < length; ++i) {
        CharacterType character = text[i];
        uint8_t substitution = character < WTF_ARRAY_LENGTH(entityMap) ? entityMap[character] : static_cast<uint8_t>(EntitySubstitutionNullIndex);
        if (UNLIKELY(substitution != EntitySubstitutionNullIndex) && entitySubstitutionList[substitution].mask & entityMask) {
            result.appendSubstring(source, offset + positionAfterLastEntity, i - positionAfterLastEntity);
            result.appendCharacters(entitySubstitutionList[substitution].characters, entitySubstitutionList[substitution].length);
            positionAfterLastEntity = i + 1;
        }
    }
    result.appendSubstring(source, offset + positionAfterLastEntity, length - positionAfterLastEntity);
}

void MarkupAccumulator::appendCharactersReplacingEntities(StringBuilder& result, const String& source, unsigned offset, unsigned length, EntityMask entityMask)
{
    ASSERT(offset + length <= source.length());

    if (!length)
        return;

    if (source.is8Bit())
        appendCharactersReplacingEntitiesInternal<LChar>(result, source, offset, length, entityMask);
    else
        appendCharactersReplacingEntitiesInternal<UChar>(result, source, offset, length, entityMask);
}

MarkupAccumulator::MarkupAccumulator(Vector<Node*>* nodes, ResolveURLs resolveURLs, SerializationSyntax serializationSyntax)
    : m_nodes(nodes)
    , m_resolveURLs(resolveURLs)
    , m_serializationSyntax(serializationSyntax)
{
}

MarkupAccumulator::~MarkupAccumulator() = default;

String MarkupAccumulator::serializeNodes(Node& targetNode, SerializedNodes root, Vector<QualifiedName>* tagNamesToSkip)
{
    serializeNodesWithNamespaces(targetNode, root, 0, tagNamesToSkip);
    return m_markup.toString();
}

void MarkupAccumulator::serializeNodesWithNamespaces(Node& targetNode, SerializedNodes root, const Namespaces* namespaces, Vector<QualifiedName>* tagNamesToSkip)
{
    if (tagNamesToSkip && is<Element>(targetNode)) {
        for (auto& name : *tagNamesToSkip) {
            if (downcast<Element>(targetNode).hasTagName(name))
                return;
        }
    }

    Namespaces namespaceHash;
    if (namespaces)
        namespaceHash = *namespaces;
    else if (inXMLFragmentSerialization()) {
        // Make sure xml prefix and namespace are always known to uphold the constraints listed at http://www.w3.org/TR/xml-names11/#xmlReserved.
        namespaceHash.set(xmlAtom().impl(), XMLNames::xmlNamespaceURI->impl());
        namespaceHash.set(XMLNames::xmlNamespaceURI->impl(), xmlAtom().impl());
    }

    if (root == SerializedNodes::SubtreeIncludingNode)
        startAppendingNode(targetNode, &namespaceHash);

    if (targetNode.document().isHTMLDocument() && elementCannotHaveEndTag(targetNode))
        return;

    Node* current = targetNode.hasTagName(templateTag) ? downcast<HTMLTemplateElement>(targetNode).content().firstChild() : targetNode.firstChild();
    for ( ; current; current = current->nextSibling())
        serializeNodesWithNamespaces(*current, SerializedNodes::SubtreeIncludingNode, &namespaceHash, tagNamesToSkip);

    if (root == SerializedNodes::SubtreeIncludingNode)
        endAppendingNode(targetNode);
}

String MarkupAccumulator::resolveURLIfNeeded(const Element& element, const String& urlString) const
{
    switch (m_resolveURLs) {
    case ResolveURLs::Yes:
        return element.document().completeURL(urlString).string();

    case ResolveURLs::YesExcludingLocalFileURLsForPrivacy:
        if (!element.document().url().isLocalFile())
            return element.document().completeURL(urlString).string();
        break;

    case ResolveURLs::No:
        break;
    }
    return urlString;
}

void MarkupAccumulator::startAppendingNode(const Node& node, Namespaces* namespaces)
{
    if (is<Element>(node))
        appendStartTag(m_markup, downcast<Element>(node), namespaces);
    else
        appendNonElementNode(m_markup, node, namespaces);

    if (m_nodes)
        m_nodes->append(const_cast<Node*>(&node));
}

void MarkupAccumulator::appendEndTag(StringBuilder& result, const Element& element)
{
    if (shouldSelfClose(element, m_serializationSyntax) || (!element.hasChildNodes() && elementCannotHaveEndTag(element)))
        return;
    result.append("</", element.nodeNamePreservingCase(), '>');
}

StringBuilder MarkupAccumulator::takeMarkup()
{
    return std::exchange(m_markup, { });
}

void MarkupAccumulator::appendAttributeValue(StringBuilder& result, const String& attribute, bool isSerializingHTML)
{
    appendCharactersReplacingEntities(result, attribute, 0, attribute.length(),
        isSerializingHTML ? EntityMaskInHTMLAttributeValue : EntityMaskInAttributeValue);
}

void MarkupAccumulator::appendCustomAttributes(StringBuilder&, const Element&, Namespaces*)
{
}

void MarkupAccumulator::appendQuotedURLAttributeValue(StringBuilder& result, const Element& element, const Attribute& attribute)
{
    ASSERT(element.isURLAttribute(attribute));
    String resolvedURLString = resolveURLIfNeeded(element, attribute.value());
    char quoteChar = '"';
    if (WTF::protocolIsJavaScript(resolvedURLString)) {
        // minimal escaping for javascript urls
        if (resolvedURLString.contains('"')) {
            if (resolvedURLString.contains('\''))
                resolvedURLString.replaceWithLiteral('"', "&quot;");
            else
                quoteChar = '\'';
        }
        result.append(quoteChar, resolvedURLString, quoteChar);
        return;
    }

    // FIXME: This does not fully match other browsers. Firefox percent-escapes non-ASCII characters for innerHTML.
    result.append(quoteChar);
    appendAttributeValue(result, resolvedURLString, false);
    result.append(quoteChar);
}

static bool shouldAddNamespaceElement(const Element& element)
{
    // Don't add namespace attribute if it is already defined for this elem.
    auto& prefix = element.prefix();
    if (prefix.isEmpty())
        return !element.hasAttribute(xmlnsAtom());
    return !element.hasAttribute("xmlns:" + prefix);
}

static bool shouldAddNamespaceAttribute(const Attribute& attribute, Namespaces& namespaces)
{
    namespaces.checkConsistency();

    // Don't add namespace attributes twice
    // HTML Parser will create xmlns attributes without namespace for HTML elements, allow those as well.
    if (attribute.name().localName() == xmlnsAtom() && (attribute.namespaceURI().isEmpty() || attribute.namespaceURI() == XMLNSNames::xmlnsNamespaceURI)) {
        namespaces.set(emptyAtom().impl(), attribute.value().impl());
        return false;
    }

    QualifiedName xmlnsPrefixAttr(xmlnsAtom(), attribute.localName(), XMLNSNames::xmlnsNamespaceURI);
    if (attribute.name() == xmlnsPrefixAttr) {
        namespaces.set(attribute.localName().impl(), attribute.value().impl());
        namespaces.set(attribute.value().impl(), attribute.localName().impl());
        return false;
    }

    return true;
}

void MarkupAccumulator::appendNamespace(StringBuilder& result, const AtomString& prefix, const AtomString& namespaceURI, Namespaces& namespaces, bool allowEmptyDefaultNS)
{
    namespaces.checkConsistency();
    if (namespaceURI.isEmpty()) {
        // http://www.whatwg.org/specs/web-apps/current-work/multipage/the-xhtml-syntax.html#xml-fragment-serialization-algorithm
        if (allowEmptyDefaultNS && namespaces.get(emptyAtom().impl()))
            result.append(' ', xmlnsAtom(), "=\"\"");
        return;
    }

    // Use emptyAtom()s's impl() for null strings since this HashMap can't handle nullptr as a key
    auto addResult = namespaces.add(prefix.isNull() ? emptyAtom().impl() : prefix.impl(), namespaceURI.impl());
    if (!addResult.isNewEntry) {
        if (addResult.iterator->value == namespaceURI.impl())
            return;
        addResult.iterator->value = namespaceURI.impl();
    }

    // Add namespace to prefix pair so we can do constraint checking later.
    if (inXMLFragmentSerialization() && !prefix.isEmpty())
        namespaces.set(namespaceURI.impl(), prefix.impl());

    // Make sure xml prefix and namespace are always known to uphold the constraints listed at http://www.w3.org/TR/xml-names11/#xmlReserved.
    if (namespaceURI == XMLNames::xmlNamespaceURI)
        return;

    result.append(' ', xmlnsAtom(), prefix.isEmpty() ? "" : ":", prefix, "=\"");
    appendAttributeValue(result, namespaceURI, false);
    result.append('"');
}

EntityMask MarkupAccumulator::entityMaskForText(const Text& text) const
{
    if (!text.document().isHTMLDocument() || inXMLFragmentSerialization())
        return EntityMaskInPCDATA;

    const QualifiedName* parentName = nullptr;
    if (text.parentElement())
        parentName = &text.parentElement()->tagQName();

    if (parentName && (*parentName == scriptTag || *parentName == styleTag || *parentName == xmpTag))
        return EntityMaskInCDATA;
    return EntityMaskInHTMLPCDATA;
}

void MarkupAccumulator::appendText(StringBuilder& result, const Text& text)
{
    appendCharactersReplacingEntities(result, text.data(), 0, text.length(), entityMaskForText(text));
}

static void appendXMLDeclaration(StringBuilder& result, const Document& document)
{
    if (!document.hasXMLDeclaration())
        return;

    auto encoding = document.xmlEncoding();
    bool isStandaloneSpecified = document.xmlStandaloneStatus() != Document::StandaloneStatus::Unspecified;

    result.append("<?xml version=\"",
        document.xmlVersion(),
        encoding.isEmpty() ? "" : "\" encoding=\"",
        encoding,
        isStandaloneSpecified ? (document.xmlStandalone() ? "\" standalone=\"yes" : "\" standalone=\"no") : "",
        "\"?>");
}

static void appendDocumentType(StringBuilder& result, const DocumentType& documentType)
{
    if (documentType.name().isEmpty())
        return;

    result.append(
        "<!DOCTYPE ",
        documentType.name(),
        documentType.publicId().isEmpty() ? "" : " PUBLIC \"",
        documentType.publicId(),
        documentType.publicId().isEmpty() ? "" : "\"",
        documentType.systemId().isEmpty() ? "" : (documentType.publicId().isEmpty() ? " SYSTEM \"" : " \""),
        documentType.systemId(),
        documentType.systemId().isEmpty() ? ">" : "\">"
    );
}

void MarkupAccumulator::appendStartTag(StringBuilder& result, const Element& element, Namespaces* namespaces)
{
    appendOpenTag(result, element, namespaces);

    if (element.hasAttributes()) {
        for (const Attribute& attribute : element.attributesIterator())
            appendAttribute(result, element, attribute, namespaces);
    }

    // Give an opportunity to subclasses to add their own attributes.
    appendCustomAttributes(result, element, namespaces);

    appendCloseTag(result, element);
}

void MarkupAccumulator::appendOpenTag(StringBuilder& result, const Element& element, Namespaces* namespaces)
{
    result.append('<');
    if (inXMLFragmentSerialization() && namespaces && element.prefix().isEmpty()) {
        // According to http://www.w3.org/TR/DOM-Level-3-Core/namespaces-algorithms.html#normalizeDocumentAlgo we now should create
        // a default namespace declaration to make this namespace well-formed. However, http://www.w3.org/TR/xml-names11/#xmlReserved states
        // "The prefix xml MUST NOT be declared as the default namespace.", so use the xml prefix explicitly.
        if (element.namespaceURI() == XMLNames::xmlNamespaceURI) {
            result.append(xmlAtom());
            result.append(':');
        }
    }
    result.append(element.nodeNamePreservingCase());
    if ((inXMLFragmentSerialization() || !element.document().isHTMLDocument()) && namespaces && shouldAddNamespaceElement(element))
        appendNamespace(result, element.prefix(), element.namespaceURI(), *namespaces, inXMLFragmentSerialization());
}

void MarkupAccumulator::appendCloseTag(StringBuilder& result, const Element& element)
{
    if (shouldSelfClose(element, m_serializationSyntax)) {
        if (element.isHTMLElement())
            result.append(' '); // XHTML 1.0 <-> HTML compatibility.
        result.append('/');
    }
    result.append('>');
}

void MarkupAccumulator::generateUniquePrefix(QualifiedName& prefixedName, const Namespaces& namespaces)
{
    // http://www.w3.org/TR/DOM-Level-3-Core/namespaces-algorithms.html#normalizeDocumentAlgo
    // Find a prefix following the pattern "NS" + index (starting at 1) and make sure this
    // prefix is not declared in the current scope.
    AtomString name;
    do {
        // FIXME: We should create makeAtomString, which would be more efficient.
        name = makeString("NS", ++m_prefixLevel);
    } while (namespaces.get(name.impl()));
    prefixedName.setPrefix(name);
}

// https://html.spec.whatwg.org/#attribute's-serialised-name
static String htmlAttributeSerialization(const Attribute& attribute)
{
    if (attribute.namespaceURI().isEmpty())
        return attribute.name().localName();

    QualifiedName prefixedName = attribute.name();
    if (attribute.namespaceURI() == XMLNames::xmlNamespaceURI)
        prefixedName.setPrefix(xmlAtom());
    else if (attribute.namespaceURI() == XMLNSNames::xmlnsNamespaceURI) {
        if (prefixedName.localName() == xmlnsAtom())
            return xmlnsAtom();
        prefixedName.setPrefix(xmlnsAtom());
    } else if (attribute.namespaceURI() == XLinkNames::xlinkNamespaceURI)
        prefixedName.setPrefix(AtomString("xlink", AtomString::ConstructFromLiteral));
    return prefixedName.toString();
}

// https://w3c.github.io/DOM-Parsing/#dfn-xml-serialization-of-the-attributes
QualifiedName MarkupAccumulator::xmlAttributeSerialization(const Attribute& attribute, Namespaces* namespaces)
{
    QualifiedName prefixedName = attribute.name();
    if (!attribute.namespaceURI().isEmpty()) {
        if (attribute.namespaceURI() == XMLNames::xmlNamespaceURI) {
            // Always use xml as prefix if the namespace is the XML namespace.
            prefixedName.setPrefix(xmlAtom());
        } else {
            AtomStringImpl* foundNS = namespaces && attribute.prefix().impl() ? namespaces->get(attribute.prefix().impl()) : nullptr;
            bool prefixIsAlreadyMappedToOtherNS = foundNS && foundNS != attribute.namespaceURI().impl();
            if (attribute.prefix().isEmpty() || !foundNS || prefixIsAlreadyMappedToOtherNS) {
                if (AtomStringImpl* prefix = namespaces ? namespaces->get(attribute.namespaceURI().impl()) : nullptr)
                    prefixedName.setPrefix(AtomString(prefix));
                else {
                    bool shouldBeDeclaredUsingAppendNamespace = !attribute.prefix().isEmpty() && !foundNS;
                    if (!shouldBeDeclaredUsingAppendNamespace && attribute.localName() != xmlnsAtom() && namespaces)
                        generateUniquePrefix(prefixedName, *namespaces);
                }
            }
        }
    }
    return prefixedName;
}

void MarkupAccumulator::appendAttribute(StringBuilder& result, const Element& element, const Attribute& attribute, Namespaces* namespaces)
{
    bool isSerializingHTML = element.document().isHTMLDocument() && !inXMLFragmentSerialization();

    result.append(' ');

    std::optional<QualifiedName> effectiveXMLPrefixedName;
    if (isSerializingHTML)
        result.append(htmlAttributeSerialization(attribute));
    else {
        effectiveXMLPrefixedName = xmlAttributeSerialization(attribute, namespaces);
        result.append(effectiveXMLPrefixedName->toString());
    }

    result.append('=');

    if (element.isURLAttribute(attribute))
        appendQuotedURLAttributeValue(result, element, attribute);
    else {
        result.append('"');
        appendAttributeValue(result, attribute.value(), isSerializingHTML);
        result.append('"');
    }

    if (!isSerializingHTML && namespaces && shouldAddNamespaceAttribute(attribute, *namespaces))
        appendNamespace(result, effectiveXMLPrefixedName->prefix(), effectiveXMLPrefixedName->namespaceURI(), *namespaces);
}

void MarkupAccumulator::appendNonElementNode(StringBuilder& result, const Node& node, Namespaces* namespaces)
{
    if (namespaces)
        namespaces->checkConsistency();

    switch (node.nodeType()) {
    case Node::TEXT_NODE:
        appendText(result, downcast<Text>(node));
        break;
    case Node::COMMENT_NODE:
        // FIXME: Comment content is not escaped, but that may be OK because XMLSerializer (and possibly other callers) should raise an exception if it includes "-->".
        result.append("<!--", downcast<Comment>(node).data(), "-->");
        break;
    case Node::DOCUMENT_NODE:
        appendXMLDeclaration(result, downcast<Document>(node));
        break;
    case Node::DOCUMENT_FRAGMENT_NODE:
        break;
    case Node::DOCUMENT_TYPE_NODE:
        appendDocumentType(result, downcast<DocumentType>(node));
        break;
    case Node::PROCESSING_INSTRUCTION_NODE:
        // FIXME: PI data is not escaped, but XMLSerializer (and possibly other callers) this should raise an exception if it includes "?>".
        result.append("<?", downcast<ProcessingInstruction>(node).target(), ' ', downcast<ProcessingInstruction>(node).data(), "?>");
        break;
    case Node::ELEMENT_NODE:
        ASSERT_NOT_REACHED();
        break;
    case Node::CDATA_SECTION_NODE:
        // FIXME: CDATA content is not escaped, but XMLSerializer (and possibly other callers) should raise an exception if it includes "]]>".
        result.append("<![CDATA[", downcast<CDATASection>(node).data(), "]]>");
        break;
    case Node::ATTRIBUTE_NODE:
        ASSERT_NOT_REACHED();
        break;
    }
}

}