Example #1
0
void SVGUseElement::expandUseElementsInShadowTree(SVGShadowTreeRootElement* shadowRoot, Node* element)
{
    // Why expand the <use> elements in the shadow tree here, and not just
    // do this directly in buildShadowTree, if we encounter a <use> element?
    //
    // Short answer: Because we may miss to expand some elements. Ie. if a <symbol>
    // contains <use> tags, we'd miss them. So once we're done with settin' up the
    // actual shadow tree (after the special case modification for svg/symbol) we have
    // to walk it completely and expand all <use> elements.
    if (element->hasTagName(SVGNames::useTag)) {
        SVGUseElement* use = static_cast<SVGUseElement*>(element);

        String id = SVGURIReference::getTarget(use->href());
        Element* targetElement = document()->getElementById(id); 
        SVGElement* target = 0;
        if (targetElement && targetElement->isSVGElement())
            target = static_cast<SVGElement*>(targetElement);

        // Don't ASSERT(target) here, it may be "pending", too.
        // Setup sub-shadow tree root node
        RefPtr<SVGShadowTreeContainerElement> cloneParent = new SVGShadowTreeContainerElement(document());

        // Spec: In the generated content, the 'use' will be replaced by 'g', where all attributes from the
        // 'use' element except for x, y, width, height and xlink:href are transferred to the generated 'g' element.
        transferUseAttributesToReplacedElement(use, cloneParent.get());

        ExceptionCode ec = 0;
        if (target && !isDisallowedElement(target)) {
            RefPtr<Element> newChild = target->cloneElementWithChildren();

            // We don't walk the target tree element-by-element, and clone each element,
            // but instead use cloneElementWithChildren(). This is an optimization for the common
            // case where <use> doesn't contain disallowed elements (ie. <foreignObject>).
            // Though if there are disallowed elements in the subtree, we have to remove them.
            // For instance: <use> on <g> containing <foreignObject> (indirect case).
            if (subtreeContainsDisallowedElement(newChild.get()))
                removeDisallowedElementsFromSubtree(newChild.get());

            SVGElement* newChildPtr = 0;
            if (newChild->isSVGElement())
                newChildPtr = static_cast<SVGElement*>(newChild.get());
            ASSERT(newChildPtr);

            cloneParent->appendChild(newChild.release(), ec);
            ASSERT(!ec);
        }

        // Replace <use> with referenced content.
        ASSERT(use->parentNode()); 
        use->parentNode()->replaceChild(cloneParent.release(), use, ec);
        ASSERT(!ec);

        // Immediately stop here, and restart expanding.
        expandUseElementsInShadowTree(shadowRoot, shadowRoot);
        return;
    }

    for (RefPtr<Node> child = element->firstChild(); child; child = child->nextSibling())
        expandUseElementsInShadowTree(shadowRoot, child.get());
}
Example #2
0
void SVGUseElement::expandUseElementsInShadowTree(Node* element)
{
    // Why expand the <use> elements in the shadow tree here, and not just
    // do this directly in buildShadowTree, if we encounter a <use> element?
    //
    // Short answer: Because we may miss to expand some elements. Ie. if a <symbol>
    // contains <use> tags, we'd miss them. So once we're done with settin' up the
    // actual shadow tree (after the special case modification for svg/symbol) we have
    // to walk it completely and expand all <use> elements.
    if (element->hasTagName(SVGNames::useTag)) {
        SVGUseElement* use = toSVGUseElement(element);
        ASSERT(!use->cachedDocumentIsStillLoading());

        ASSERT(referencedDocument());
        Element* targetElement = SVGURIReference::targetElementFromIRIString(use->href(), *referencedDocument());
        SVGElement* target = 0;
        if (targetElement && targetElement->isSVGElement())
            target = toSVGElement(targetElement);

        // Don't ASSERT(target) here, it may be "pending", too.
        // Setup sub-shadow tree root node
        RefPtr<SVGGElement> cloneParent = SVGGElement::create(SVGNames::gTag, *referencedDocument());
        use->cloneChildNodes(cloneParent.get());

        // Spec: In the generated content, the 'use' will be replaced by 'g', where all attributes from the
        // 'use' element except for x, y, width, height and xlink:href are transferred to the generated 'g' element.
        transferUseAttributesToReplacedElement(use, cloneParent.get());

        if (target && !isDisallowedElement(*target)) {
            RefPtr<Element> newChild = target->cloneElementWithChildren();
            ASSERT(newChild->isSVGElement());
            cloneParent->appendChild(newChild.release());
        }

        // We don't walk the target tree element-by-element, and clone each element,
        // but instead use cloneElementWithChildren(). This is an optimization for the common
        // case where <use> doesn't contain disallowed elements (ie. <foreignObject>).
        // Though if there are disallowed elements in the subtree, we have to remove them.
        // For instance: <use> on <g> containing <foreignObject> (indirect case).
        if (subtreeContainsDisallowedElement(*cloneParent))
            removeDisallowedElementsFromSubtree(*cloneParent);

        RefPtr<Node> replacingElement(cloneParent.get());

        // Replace <use> with referenced content.
        ASSERT(use->parentNode());
        use->parentNode()->replaceChild(cloneParent.release(), use);

        // Expand the siblings because the *element* is replaced and we will
        // lose the sibling chain when we are back from recursion.
        element = replacingElement.get();
        for (RefPtr<Node> sibling = element->nextSibling(); sibling; sibling = sibling->nextSibling())
            expandUseElementsInShadowTree(sibling.get());
    }

    for (RefPtr<Node> child = element->firstChild(); child; child = child->nextSibling())
        expandUseElementsInShadowTree(child.get());
}
void SVGUseElement::buildShadowAndInstanceTree(SVGElement* target)
{
    ASSERT(!m_targetElementInstance);
    ASSERT(!m_needsShadowTreeRecreation);

    // <use> creates a "user agent" shadow root. Do not build the shadow/instance tree for <use>
    // elements living in a user agent shadow tree because they will get expanded in a second
    // pass -- see expandUseElementsInShadowTree().
    if (inUseShadowTree())
        return;

    // Do not allow self-referencing.
    // 'target' may be null, if it's a non SVG namespaced element.
    if (!target || target == this || isDisallowedElement(target))
        return;

    // Set up root SVG element in shadow tree.
    RefPtrWillBeRawPtr<Element> newChild = target->cloneElementWithoutChildren();
    m_targetElementInstance = toSVGElement(newChild.get());
    ShadowRoot* shadowTreeRootElement = userAgentShadowRoot();
    shadowTreeRootElement->appendChild(newChild.release());

    // Clone the target subtree into the shadow tree, not handling <use> and <symbol> yet.

    // SVG specification does not say a word about <use> & cycles. My view on this is: just ignore it!
    // Non-appearing <use> content is easier to debug, then half-appearing content.
    if (!buildShadowTree(target, m_targetElementInstance.get(), false)) {
        clearShadowTree();
        return;
    }

    if (instanceTreeIsLoading(m_targetElementInstance.get()))
        return;

    // Assure shadow tree building was successfull
    ASSERT(m_targetElementInstance);
    ASSERT(m_targetElementInstance->correspondingUseElement() == this);
    ASSERT(m_targetElementInstance->correspondingElement() == target);

    // Expand all <use> elements in the shadow tree.
    // Expand means: replace the actual <use> element by what it references.
    if (!expandUseElementsInShadowTree(m_targetElementInstance.get())) {
        clearShadowTree();
        return;
    }

    // Expand all <symbol> elements in the shadow tree.
    // Expand means: replace the actual <symbol> element by the <svg> element.
    expandSymbolElementsInShadowTree(toSVGElement(shadowTreeRootElement->firstChild()));

    m_targetElementInstance = toSVGElement(shadowTreeRootElement->firstChild());
    transferUseWidthAndHeightIfNeeded(*this, m_targetElementInstance.get(), *m_targetElementInstance->correspondingElement());

    ASSERT(m_targetElementInstance->parentNode() == shadowTreeRootElement);

    // Update relative length information.
    updateRelativeLengthsInformation();
}
Example #4
0
void SVGUseElement::buildShadowAndInstanceTree(SVGShadowTreeRootElement* shadowRoot)
{
    String id = SVGURIReference::getTarget(href());
    Element* targetElement = document()->getElementById(id);
    if (!targetElement) {
        // The only time we should get here is when the use element has not been
        // given a resource to target.
        ASSERT(m_resourceId.isEmpty());
        return;
    }

    // Do not build the shadow/instance tree for <use> elements living in a shadow tree.
    // The will be expanded soon anyway - see expandUseElementsInShadowTree().
    Node* parent = parentNode();
    while (parent) {
        if (parent->isShadowNode())
            return;

        parent = parent->parentNode();
    }
 
    SVGElement* target = 0;
    if (targetElement && targetElement->isSVGElement())
        target = static_cast<SVGElement*>(targetElement);

    if (m_targetElementInstance)
        m_targetElementInstance = 0;

    // Do not allow self-referencing.
    // 'target' may be null, if it's a non SVG namespaced element.
    if (!target || target == this)
        return;

    // Why a seperated instance/shadow tree? SVG demands it:
    // The instance tree is accesable from JavaScript, and has to
    // expose a 1:1 copy of the referenced tree, whereas internally we need
    // to alter the tree for correct "use-on-symbol", "use-on-svg" support.  
 
    // Build instance tree. Create root SVGElementInstance object for the first sub-tree node.
    //
    // Spec: If the 'use' element references a simple graphics element such as a 'rect', then there is only a
    // single SVGElementInstance object, and the correspondingElement attribute on this SVGElementInstance object
    // is the SVGRectElement that corresponds to the referenced 'rect' element.
    m_targetElementInstance = SVGElementInstance::create(this, target);

    // Eventually enter recursion to build SVGElementInstance objects for the sub-tree children
    bool foundProblem = false;
    buildInstanceTree(target, m_targetElementInstance.get(), foundProblem);

    // SVG specification does not say a word about <use> & cycles. My view on this is: just ignore it!
    // Non-appearing <use> content is easier to debug, then half-appearing content.
    if (foundProblem) {
        m_targetElementInstance = 0;
        return;
    }

    // Assure instance tree building was successfull
    ASSERT(m_targetElementInstance);
    ASSERT(!m_targetElementInstance->shadowTreeElement());
    ASSERT(m_targetElementInstance->correspondingUseElement() == this);
    ASSERT(m_targetElementInstance->correspondingElement() == target);

    // Build shadow tree from instance tree
    // This also handles the special cases: <use> on <symbol>, <use> on <svg>.
    buildShadowTree(shadowRoot, target, m_targetElementInstance.get());

#if ENABLE(SVG) && ENABLE(SVG_USE)
    // Expand all <use> elements in the shadow tree.
    // Expand means: replace the actual <use> element by what it references.
    expandUseElementsInShadowTree(shadowRoot, shadowRoot);

    // Expand all <symbol> elements in the shadow tree.
    // Expand means: replace the actual <symbol> element by the <svg> element.
    expandSymbolElementsInShadowTree(shadowRoot, shadowRoot);
#endif

    // Now that the shadow tree is completly expanded, we can associate
    // shadow tree elements <-> instances in the instance tree.
    associateInstancesWithShadowTreeElements(shadowRoot->firstChild(), m_targetElementInstance.get());

    // If no shadow tree element is present, this means that the reference root
    // element was removed, as it is disallowed (ie. <use> on <foreignObject>)
    // Do NOT leave an inconsistent instance tree around, instead destruct it.
    if (!m_targetElementInstance->shadowTreeElement()) {
        shadowRoot->removeAllChildren();
        m_targetElementInstance = 0;
        return;
    }

    // Consistency checks - this is assumed in updateContainerOffset().
    ASSERT(m_targetElementInstance->shadowTreeElement()->parentNode() == shadowRoot);

    // Eventually dump instance tree
#ifdef DUMP_INSTANCE_TREE
    String text;
    unsigned int depth = 0;

    dumpInstanceTree(depth, text, m_targetElementInstance.get());
    fprintf(stderr, "\nDumping <use> instance tree:\n%s\n", text.latin1().data());
#endif

    // Eventually dump shadow tree
#ifdef DUMP_SHADOW_TREE
    ExceptionCode ec = 0;

    PassRefPtr<XMLSerializer> serializer = XMLSerializer::create();

    String markup = serializer->serializeToString(shadowRoot, ec);
    ASSERT(!ec);

    fprintf(stderr, "Dumping <use> shadow tree markup:\n%s\n", markup.latin1().data());
#endif

    // Transfer event listeners assigned to the referenced element to our shadow tree elements.
    transferEventListenersToShadowTree(m_targetElementInstance.get());

    // Update container offset/size
    updateContainerOffsets();
    updateContainerSizes();
}
bool SVGUseElement::expandUseElementsInShadowTree(SVGElement* element)
{
    ASSERT(element);
    // Why expand the <use> elements in the shadow tree here, and not just
    // do this directly in buildShadowTree, if we encounter a <use> element?
    //
    // Short answer: Because we may miss to expand some elements. For example, if a <symbol>
    // contains <use> tags, we'd miss them. So once we're done with setting up the
    // actual shadow tree (after the special case modification for svg/symbol) we have
    // to walk it completely and expand all <use> elements.
    if (isSVGUseElement(*element)) {
        SVGUseElement* use = toSVGUseElement(element);
        ASSERT(!use->resourceIsStillLoading());

        SVGElement* target = 0;
        if (hasCycleUseReferencing(toSVGUseElement(use->correspondingElement()), use, target))
            return false;

        if (target && isDisallowedElement(target))
            return false;
        // Don't ASSERT(target) here, it may be "pending", too.
        // Setup sub-shadow tree root node
        RefPtrWillBeRawPtr<SVGGElement> cloneParent = SVGGElement::create(referencedScope()->document());
        cloneParent->setCorrespondingElement(use->correspondingElement());

        // Move already cloned elements to the new <g> element
        for (RefPtrWillBeRawPtr<Node> child = use->firstChild(); child; ) {
            RefPtrWillBeRawPtr<Node> nextChild = child->nextSibling();
            cloneParent->appendChild(child);
            child = nextChild.release();
        }

        // Spec: In the generated content, the 'use' will be replaced by 'g', where all attributes from the
        // 'use' element except for x, y, width, height and xlink:href are transferred to the generated 'g' element.
        transferUseAttributesToReplacedElement(use, cloneParent.get());

        if (target) {
            RefPtrWillBeRawPtr<Node> newChild = cloneNodeAndAssociate(*target);
            ASSERT(newChild->isSVGElement());
            transferUseWidthAndHeightIfNeeded(*use, toSVGElement(newChild.get()), *target);
            cloneParent->appendChild(newChild.release());
        }

        // We don't walk the target tree element-by-element, and clone each element,
        // but instead use cloneElementWithChildren(). This is an optimization for the common
        // case where <use> doesn't contain disallowed elements (ie. <foreignObject>).
        // Though if there are disallowed elements in the subtree, we have to remove them.
        // For instance: <use> on <g> containing <foreignObject> (indirect case).
        if (subtreeContainsDisallowedElement(cloneParent.get()))
            removeDisallowedElementsFromSubtree(*cloneParent);

        RefPtrWillBeRawPtr<SVGElement> replacingElement(cloneParent.get());

        // Replace <use> with referenced content.
        ASSERT(use->parentNode());
        use->parentNode()->replaceChild(cloneParent.release(), use);

        // Expand the siblings because the *element* is replaced and we will
        // lose the sibling chain when we are back from recursion.
        element = replacingElement.get();
        for (RefPtrWillBeRawPtr<SVGElement> sibling = Traversal<SVGElement>::nextSibling(*element); sibling; sibling = Traversal<SVGElement>::nextSibling(*sibling)) {
            if (!expandUseElementsInShadowTree(sibling.get()))
                return false;
        }
    }

    for (RefPtrWillBeRawPtr<SVGElement> child = Traversal<SVGElement>::firstChild(*element); child; child = Traversal<SVGElement>::nextSibling(*child)) {
        if (!expandUseElementsInShadowTree(child.get()))
            return false;
    }
    return true;
}
Example #6
0
void SVGUseElement::buildShadowAndInstanceTree(SVGElement* target)
{
    ASSERT(!m_targetElementInstance);

    // Do not build the shadow/instance tree for <use> elements living in a shadow tree.
    // The will be expanded soon anyway - see expandUseElementsInShadowTree().
    if (isInShadowTree())
        return;

    // Do not allow self-referencing.
    // 'target' may be null, if it's a non SVG namespaced element.
    if (!target || target == this)
        return;

    // Why a seperated instance/shadow tree? SVG demands it:
    // The instance tree is accesable from JavaScript, and has to
    // expose a 1:1 copy of the referenced tree, whereas internally we need
    // to alter the tree for correct "use-on-symbol", "use-on-svg" support.

    // Build instance tree. Create root SVGElementInstance object for the first sub-tree node.
    //
    // Spec: If the 'use' element references a simple graphics element such as a 'rect', then there is only a
    // single SVGElementInstance object, and the correspondingElement attribute on this SVGElementInstance object
    // is the SVGRectElement that corresponds to the referenced 'rect' element.
    m_targetElementInstance = SVGElementInstance::create(this, this, target);

    // Eventually enter recursion to build SVGElementInstance objects for the sub-tree children
    bool foundProblem = false;
    buildInstanceTree(target, m_targetElementInstance.get(), foundProblem, false);

    if (instanceTreeIsLoading(m_targetElementInstance.get()))
        return;

    // SVG specification does not say a word about <use> & cycles. My view on this is: just ignore it!
    // Non-appearing <use> content is easier to debug, then half-appearing content.
    if (foundProblem) {
        clearResourceReferences();
        return;
    }

    // Assure instance tree building was successfull
    ASSERT(m_targetElementInstance);
    ASSERT(!m_targetElementInstance->shadowTreeElement());
    ASSERT(m_targetElementInstance->correspondingUseElement() == this);
    ASSERT(m_targetElementInstance->directUseElement() == this);
    ASSERT(m_targetElementInstance->correspondingElement() == target);

    ShadowRoot* shadowTreeRootElement = shadowRoot();
    ASSERT(shadowTreeRootElement);

    // Build shadow tree from instance tree
    // This also handles the special cases: <use> on <symbol>, <use> on <svg>.
    buildShadowTree(target, m_targetElementInstance.get());

    // Expand all <use> elements in the shadow tree.
    // Expand means: replace the actual <use> element by what it references.
    expandUseElementsInShadowTree(shadowTreeRootElement);

    // Expand all <symbol> elements in the shadow tree.
    // Expand means: replace the actual <symbol> element by the <svg> element.
    expandSymbolElementsInShadowTree(shadowTreeRootElement);

    // Now that the shadow tree is completly expanded, we can associate
    // shadow tree elements <-> instances in the instance tree.
    associateInstancesWithShadowTreeElements(shadowTreeRootElement->firstChild(), m_targetElementInstance.get());

    // If no shadow tree element is present, this means that the reference root
    // element was removed, as it is disallowed (ie. <use> on <foreignObject>)
    // Do NOT leave an inconsistent instance tree around, instead destruct it.
    if (!m_targetElementInstance->shadowTreeElement()) {
        clearResourceReferences();
        return;
    }

    ASSERT(m_targetElementInstance->shadowTreeElement()->parentNode() == shadowTreeRootElement);

    // Transfer event listeners assigned to the referenced element to our shadow tree elements.
    transferEventListenersToShadowTree(m_targetElementInstance.get());

    // Update relative length information.
    updateRelativeLengthsInformation();

    // Eventually dump instance tree
#ifdef DUMP_INSTANCE_TREE
    String text;
    unsigned int depth = 0;

    dumpInstanceTree(depth, text, m_targetElementInstance.get());
    fprintf(stderr, "\nDumping <use> instance tree:\n%s\n", text.latin1().data());
#endif

    // Eventually dump shadow tree
#ifdef DUMP_SHADOW_TREE
    RefPtr<XMLSerializer> serializer = XMLSerializer::create();
    String markup = serializer->serializeToString(shadowTreeRootElement, ASSERT_NO_EXCEPTION);
    fprintf(stderr, "Dumping <use> shadow tree markup:\n%s\n", markup.latin1().data());
#endif
}
Example #7
0
void SVGUseElement::expandUseElementsInShadowTree(Node* element)
{
    // Why expand the <use> elements in the shadow tree here, and not just
    // do this directly in buildShadowTree, if we encounter a <use> element?
    //
    // Short answer: Because we may miss to expand some elements. Ie. if a <symbol>
    // contains <use> tags, we'd miss them. So once we're done with settin' up the
    // actual shadow tree (after the special case modification for svg/symbol) we have
    // to walk it completely and expand all <use> elements.
    if (element->hasTagName(SVGNames::useTag)) {
        SVGUseElement* use = static_cast<SVGUseElement*>(element);

        String id = SVGURIReference::getTarget(use->href());
        Element* targetElement = document()->getElementById(id); 
        SVGElement* target = 0;
        if (targetElement && targetElement->isSVGElement())
            target = static_cast<SVGElement*>(targetElement);

        // Don't ASSERT(target) here, it may be "pending", too.
        if (target) {
            // Setup sub-shadow tree root node
            RefPtr<SVGElement> cloneParent = new SVGGElement(SVGNames::gTag, document());

            // Spec: In the generated content, the 'use' will be replaced by 'g', where all attributes from the
            // 'use' element except for x, y, width, height and xlink:href are transferred to the generated 'g' element.
            transferUseAttributesToReplacedElement(use, cloneParent.get());

            // Spec: An additional transformation translate(x,y) is appended to the end
            // (i.e., right-side) of the transform attribute on the generated 'g', where x
            // and y represent the values of the x and y attributes on the 'use' element.
            if (use->x().value() != 0.0 || use->y().value() != 0.0) {
                if (!cloneParent->hasAttribute(SVGNames::transformAttr)) {
                    String transformString = String::format("translate(%f, %f)", use->x().value(), use->y().value());
                    cloneParent->setAttribute(SVGNames::transformAttr, transformString);
                } else {
                    String transformString = String::format(" translate(%f, %f)", use->x().value(), use->y().value());
                    const AtomicString& transformAttribute = cloneParent->getAttribute(SVGNames::transformAttr);
                    cloneParent->setAttribute(SVGNames::transformAttr, transformAttribute + transformString); 
                }
            }

            ExceptionCode ec = 0;
 
            // For instance <use> on <foreignObject> (direct case).
            if (isDisallowedElement(target)) {
                // We still have to setup the <use> replacment (<g>). Otherwhise
                // associateInstancesWithShadowTreeElements() makes wrong assumptions.
                // Replace <use> with referenced content.
                ASSERT(use->parentNode()); 
                use->parentNode()->replaceChild(cloneParent.release(), use, ec);
                ASSERT(ec == 0);
                return;
            }

            RefPtr<Node> newChild = target->cloneNode(true);

            // We don't walk the target tree element-by-element, and clone each element,
            // but instead use cloneNode(deep=true). This is an optimization for the common
            // case where <use> doesn't contain disallowed elements (ie. <foreignObject>).
            // Though if there are disallowed elements in the subtree, we have to remove them.
            // For instance: <use> on <g> containing <foreignObject> (indirect case).
            if (subtreeContainsDisallowedElement(newChild.get()))
                removeDisallowedElementsFromSubtree(newChild.get());

            SVGElement* newChildPtr = 0;
            if (newChild->isSVGElement())
                newChildPtr = static_cast<SVGElement*>(newChild.get());
            ASSERT(newChildPtr);

            cloneParent->appendChild(newChild.release(), ec);
            ASSERT(ec == 0);

            // Replace <use> with referenced content.
            ASSERT(use->parentNode()); 
            use->parentNode()->replaceChild(cloneParent.release(), use, ec);
            ASSERT(ec == 0);

            // Handle use referencing <svg> special case
            if (target->hasTagName(SVGNames::svgTag))
                alterShadowTreeForSVGTag(newChildPtr);

            // Immediately stop here, and restart expanding.
            expandUseElementsInShadowTree(m_shadowTreeRootElement.get());
            return;
        }
    }

    for (RefPtr<Node> child = element->firstChild(); child; child = child->nextSibling())
        expandUseElementsInShadowTree(child.get());
}
Example #8
0
void SVGUseElement::buildPendingResource()
{
    String id = SVGURIReference::getTarget(href());
    Element* targetElement = document()->getElementById(id);

    if (!targetElement) {
        // TODO: We want to deregister as pending resource, if our href() changed!
        // TODO: Move to svgAttributeChanged, once we're fixing use & the new dynamic update concept.
        document()->accessSVGExtensions()->addPendingResource(id, this);
        return;
    }

    // Do not build the shadow/instance tree for <use> elements living in a shadow tree.
    // The will be expanded soon anyway - see expandUseElementsInShadowTree().
    Node* parent = parentNode();
    while (parent) {
        if (parent->isShadowNode())
            return;

        parent = parent->parentNode();
    }
 
    SVGElement* target = 0;
    if (targetElement && targetElement->isSVGElement())
        target = static_cast<SVGElement*>(targetElement);

    // Do not allow self-referencing.
    // 'target' may be null, if it's a non SVG namespaced element.
    if (!target || target == this) {
        m_targetElementInstance = 0;
        m_shadowTreeRootElement = 0;
        return;
    }

    // Why a seperated instance/shadow tree? SVG demands it:
    // The instance tree is accesable from JavaScript, and has to
    // expose a 1:1 copy of the referenced tree, whereas internally we need
    // to alter the tree for correct "use-on-symbol", "use-on-svg" support.  
 
    // Build instance tree. Create root SVGElementInstance object for the first sub-tree node.
    //
    // Spec: If the 'use' element references a simple graphics element such as a 'rect', then there is only a
    // single SVGElementInstance object, and the correspondingElement attribute on this SVGElementInstance object
    // is the SVGRectElement that corresponds to the referenced 'rect' element.
    m_targetElementInstance = new SVGElementInstance(this, target);

    // Eventually enter recursion to build SVGElementInstance objects for the sub-tree children
    bool foundProblem = false;
    buildInstanceTree(target, m_targetElementInstance.get(), foundProblem);

    // SVG specification does not say a word about <use> & cycles. My view on this is: just ignore it!
    // Non-appearing <use> content is easier to debug, then half-appearing content.
    if (foundProblem) {
        m_targetElementInstance = 0;
        m_shadowTreeRootElement = 0;
        return;
    }

    // Assure instance tree building was successfull
    ASSERT(m_targetElementInstance);
    ASSERT(m_targetElementInstance->correspondingUseElement() == this);

    // Setup shadow tree root node
    m_shadowTreeRootElement = new SVGGElement(SVGNames::gTag, document());
    m_shadowTreeRootElement->setInDocument();
    m_shadowTreeRootElement->setShadowParentNode(this);

    // Spec: An additional transformation translate(x,y) is appended to the end
    // (i.e., right-side) of the transform attribute on the generated 'g', where x
    // and y represent the values of the x and y attributes on the 'use' element. 
    if (x().value() != 0.0 || y().value() != 0.0) {
        String transformString = String::format("translate(%f, %f)", x().value(), y().value());
        m_shadowTreeRootElement->setAttribute(SVGNames::transformAttr, transformString);
    }

    // Build shadow tree from instance tree
    // This also handles the special cases: <use> on <symbol>, <use> on <svg>.
    buildShadowTree(target, m_targetElementInstance.get());

#if ENABLE(SVG) && ENABLE(SVG_USE)
    // Expand all <use> elements in the shadow tree.
    // Expand means: replace the actual <use> element by what it references.
    expandUseElementsInShadowTree(m_shadowTreeRootElement.get());

    // Expand all <symbol> elements in the shadow tree.
    // Expand means: replace the actual <symbol> element by the <svg> element.
    expandSymbolElementsInShadowTree(m_shadowTreeRootElement.get());

#endif

    // Now that the shadow tree is completly expanded, we can associate
    // shadow tree elements <-> instances in the instance tree.
    associateInstancesWithShadowTreeElements(m_shadowTreeRootElement->firstChild(), m_targetElementInstance.get());

    // Eventually dump instance tree
#ifdef DUMP_INSTANCE_TREE
    String text;
    unsigned int depth = 0;

    dumpInstanceTree(depth, text, m_targetElementInstance.get());
    fprintf(stderr, "\nDumping <use> instance tree:\n%s\n", text.latin1().data());
#endif

    // Eventually dump shadow tree
#ifdef DUMP_SHADOW_TREE
    ExceptionCode ec = 0;

    PassRefPtr<XMLSerializer> serializer = XMLSerializer::create();

    String markup = serializer->serializeToString(m_shadowTreeRootElement.get(), ec);
    ASSERT(ec == 0);

    fprintf(stderr, "Dumping <use> shadow tree markup:\n%s\n", markup.latin1().data());
#endif

    // The DOM side is setup properly. Now we have to attach the root shadow
    // tree element manually - using attach() won't work for "shadow nodes".
    attachShadowTree();
}