/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! Element nodes.

use devtools_traits::AttrInfo;
use crate::dom::activation::Activatable;
use crate::dom::attr::{Attr, AttrHelpersForLayout};
use crate::dom::bindings::cell::DomRefCell;
use crate::dom::bindings::codegen::Bindings::AttrBinding::AttrMethods;
use crate::dom::bindings::codegen::Bindings::DocumentBinding::DocumentMethods;
use crate::dom::bindings::codegen::Bindings::ElementBinding;
use crate::dom::bindings::codegen::Bindings::ElementBinding::ElementMethods;
use crate::dom::bindings::codegen::Bindings::EventBinding::EventMethods;
use crate::dom::bindings::codegen::Bindings::FunctionBinding::Function;
use crate::dom::bindings::codegen::Bindings::HTMLTemplateElementBinding::HTMLTemplateElementMethods;
use crate::dom::bindings::codegen::Bindings::NodeBinding::NodeMethods;
use crate::dom::bindings::codegen::Bindings::WindowBinding::{ScrollBehavior, ScrollToOptions};
use crate::dom::bindings::codegen::Bindings::WindowBinding::WindowMethods;
use crate::dom::bindings::codegen::UnionTypes::NodeOrString;
use crate::dom::bindings::conversions::DerivedFrom;
use crate::dom::bindings::error::{Error, ErrorResult, Fallible};
use crate::dom::bindings::inheritance::{Castable, ElementTypeId, HTMLElementTypeId, NodeTypeId};
use crate::dom::bindings::refcounted::{Trusted, TrustedPromise};
use crate::dom::bindings::reflector::DomObject;
use crate::dom::bindings::root::{Dom, DomRoot, LayoutDom, MutNullableDom, RootedReference};
use crate::dom::bindings::str::DOMString;
use crate::dom::bindings::xmlname::{namespace_from_domstring, validate_and_extract, xml_name_type};
use crate::dom::bindings::xmlname::XMLName::InvalidXMLName;
use crate::dom::characterdata::CharacterData;
use crate::dom::create::create_element;
use crate::dom::customelementregistry::{CallbackReaction, CustomElementDefinition, CustomElementReaction};
use crate::dom::document::{Document, LayoutDocumentHelpers};
use crate::dom::documentfragment::DocumentFragment;
use crate::dom::domrect::DOMRect;
use crate::dom::domtokenlist::DOMTokenList;
use crate::dom::event::Event;
use crate::dom::eventtarget::EventTarget;
use crate::dom::htmlanchorelement::HTMLAnchorElement;
use crate::dom::htmlbodyelement::{HTMLBodyElement, HTMLBodyElementLayoutHelpers};
use crate::dom::htmlbuttonelement::HTMLButtonElement;
use crate::dom::htmlcanvaselement::{HTMLCanvasElement, LayoutHTMLCanvasElementHelpers};
use crate::dom::htmlcollection::HTMLCollection;
use crate::dom::htmlelement::HTMLElement;
use crate::dom::htmlfieldsetelement::HTMLFieldSetElement;
use crate::dom::htmlfontelement::{HTMLFontElement, HTMLFontElementLayoutHelpers};
use crate::dom::htmlformelement::FormControlElementHelpers;
use crate::dom::htmlhrelement::{HTMLHRElement, HTMLHRLayoutHelpers};
use crate::dom::htmliframeelement::{HTMLIFrameElement, HTMLIFrameElementLayoutMethods};
use crate::dom::htmlimageelement::{HTMLImageElement, LayoutHTMLImageElementHelpers};
use crate::dom::htmlinputelement::{HTMLInputElement, LayoutHTMLInputElementHelpers};
use crate::dom::htmllabelelement::HTMLLabelElement;
use crate::dom::htmllegendelement::HTMLLegendElement;
use crate::dom::htmllinkelement::HTMLLinkElement;
use crate::dom::htmlobjectelement::HTMLObjectElement;
use crate::dom::htmloptgroupelement::HTMLOptGroupElement;
use crate::dom::htmlselectelement::HTMLSelectElement;
use crate::dom::htmlstyleelement::HTMLStyleElement;
use crate::dom::htmltablecellelement::{HTMLTableCellElement, HTMLTableCellElementLayoutHelpers};
use crate::dom::htmltableelement::{HTMLTableElement, HTMLTableElementLayoutHelpers};
use crate::dom::htmltablerowelement::{HTMLTableRowElement, HTMLTableRowElementLayoutHelpers};
use crate::dom::htmltablesectionelement::{HTMLTableSectionElement, HTMLTableSectionElementLayoutHelpers};
use crate::dom::htmltemplateelement::HTMLTemplateElement;
use crate::dom::htmltextareaelement::{HTMLTextAreaElement, LayoutHTMLTextAreaElementHelpers};
use crate::dom::mutationobserver::{Mutation, MutationObserver};
use crate::dom::namednodemap::NamedNodeMap;
use crate::dom::node::{ChildrenMutation, LayoutNodeHelpers, Node};
use crate::dom::node::{NodeDamage, NodeFlags, UnbindContext};
use crate::dom::node::{document_from_node, window_from_node};
use crate::dom::nodelist::NodeList;
use crate::dom::promise::Promise;
use crate::dom::servoparser::ServoParser;
use crate::dom::text::Text;
use crate::dom::validation::Validatable;
use crate::dom::virtualmethods::{VirtualMethods, vtable_for};
use crate::dom::window::ReflowReason;
use dom_struct::dom_struct;
use html5ever::{Prefix, LocalName, Namespace, QualName};
use html5ever::serialize;
use html5ever::serialize::SerializeOpts;
use html5ever::serialize::TraversalScope;
use html5ever::serialize::TraversalScope::{ChildrenOnly, IncludeNode};
use js::jsapi::Heap;
use js::jsval::JSVal;
use msg::constellation_msg::InputMethodType;
use net_traits::request::CorsSettings;
use ref_filter_map::ref_filter_map;
use script_layout_interface::message::ReflowGoal;
use crate::script_thread::ScriptThread;
use selectors::Element as SelectorsElement;
use selectors::attr::{AttrSelectorOperation, NamespaceConstraint, CaseSensitivity};
use selectors::matching::{ElementSelectorFlags, MatchingContext};
use selectors::sink::Push;
use servo_arc::Arc;
use servo_atoms::Atom;
use std::borrow::Cow;
use std::cell::{Cell, Ref};
use std::default::Default;
use std::fmt;
use std::mem;
use std::rc::Rc;
use std::str::FromStr;
use style::CaseSensitivityExt;
use style::applicable_declarations::ApplicableDeclarationBlock;
use style::attr::{AttrValue, LengthOrPercentageOrAuto};
use style::context::QuirksMode;
use style::dom_apis;
use style::element_state::ElementState;
use style::invalidation::element::restyle_hints::RestyleHint;
use style::properties::{ComputedValues, Importance, PropertyDeclaration};
use style::properties::{PropertyDeclarationBlock, parse_style_attribute};
use style::properties::longhands::{self, background_image, border_spacing, font_family, font_size};
use style::properties::longhands::{overflow_x, overflow_y};
use style::rule_tree::CascadeLevel;
use style::selector_parser::{NonTSPseudoClass, PseudoElement, RestyleDamage, SelectorImpl, SelectorParser};
use style::selector_parser::extended_filtering;
use style::shared_lock::{SharedRwLock, Locked};
use style::thread_state;
use style::values::{CSSFloat, Either};
use style::values::{specified, computed};
use crate::stylesheet_loader::StylesheetOwner;
use crate::task::TaskOnce;
use xml5ever::serialize as xmlSerialize;
use xml5ever::serialize::SerializeOpts as XmlSerializeOpts;
use xml5ever::serialize::TraversalScope as XmlTraversalScope;
use xml5ever::serialize::TraversalScope::ChildrenOnly as XmlChildrenOnly;
use xml5ever::serialize::TraversalScope::IncludeNode as XmlIncludeNode;

// TODO: Update focus state when the top-level browsing context gains or loses system focus,
// and when the element enters or leaves a browsing context container.
// https://html.spec.whatwg.org/multipage/#selector-focus

#[dom_struct]
pub struct Element {
    node: Node,
    local_name: LocalName,
    tag_name: TagName,
    namespace: Namespace,
    prefix: DomRefCell<Option<Prefix>>,
    attrs: DomRefCell<Vec<Dom<Attr>>>,
    id_attribute: DomRefCell<Option<Atom>>,
    is: DomRefCell<Option<LocalName>>,
    #[ignore_malloc_size_of = "Arc"]
    style_attribute: DomRefCell<Option<Arc<Locked<PropertyDeclarationBlock>>>>,
    attr_list: MutNullableDom<NamedNodeMap>,
    class_list: MutNullableDom<DOMTokenList>,
    state: Cell<ElementState>,
    /// These flags are set by the style system to indicate the that certain
    /// operations may require restyling this element or its descendants. The
    /// flags are not atomic, so the style system takes care of only set them
    /// when it has exclusive access to the element.
    #[ignore_malloc_size_of = "bitflags defined in rust-selectors"]
    selector_flags: Cell<ElementSelectorFlags>,
    /// <https://html.spec.whatwg.org/multipage/#custom-element-reaction-queue>
    custom_element_reaction_queue: DomRefCell<Vec<CustomElementReaction>>,
    /// <https://dom.spec.whatwg.org/#concept-element-custom-element-definition>
    #[ignore_malloc_size_of = "Rc"]
    custom_element_definition: DomRefCell<Option<Rc<CustomElementDefinition>>>,
    /// <https://dom.spec.whatwg.org/#concept-element-custom-element-state>
    custom_element_state: Cell<CustomElementState>,
}

impl fmt::Debug for Element {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "<{}", self.local_name)?;
        if let Some(ref id) = *self.id_attribute.borrow() {
            write!(f, " id={}", id)?;
        }
        write!(f, ">")
    }
}

impl fmt::Debug for DomRoot<Element> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        (**self).fmt(f)
    }
}

#[derive(MallocSizeOf, PartialEq)]
pub enum ElementCreator {
    ParserCreated(u64),
    ScriptCreated,
}

pub enum CustomElementCreationMode {
    Synchronous,
    Asynchronous,
}

/// <https://dom.spec.whatwg.org/#concept-element-custom-element-state>
#[derive(Clone, Copy, Eq, JSTraceable, MallocSizeOf, PartialEq)]
pub enum CustomElementState {
    Undefined,
    Failed,
    Uncustomized,
    Custom,
}

impl ElementCreator {
    pub fn is_parser_created(&self) -> bool {
        match *self {
            ElementCreator::ParserCreated(_) => true,
            ElementCreator::ScriptCreated => false,
        }
    }
    pub fn return_line_number(&self) -> u64 {
        match *self {
            ElementCreator::ParserCreated(l) => l,
            ElementCreator::ScriptCreated => 1,
        }
    }
}

pub enum AdjacentPosition {
    BeforeBegin,
    AfterEnd,
    AfterBegin,
    BeforeEnd,
}

impl FromStr for AdjacentPosition {
    type Err = Error;

    fn from_str(position: &str) -> Result<Self, Self::Err> {
        match_ignore_ascii_case! { &*position,
            "beforebegin" => Ok(AdjacentPosition::BeforeBegin),
            "afterbegin"  => Ok(AdjacentPosition::AfterBegin),
            "beforeend"   => Ok(AdjacentPosition::BeforeEnd),
            "afterend"    => Ok(AdjacentPosition::AfterEnd),
            _             => Err(Error::Syntax)
        }
    }
}

//
// Element methods
//
impl Element {
    pub fn create(
        name: QualName,
        is: Option<LocalName>,
        document: &Document,
        creator: ElementCreator,
        mode: CustomElementCreationMode,
    ) -> DomRoot<Element> {
        create_element(name, is, document, creator, mode)
    }

    pub fn new_inherited(
        local_name: LocalName,
        namespace: Namespace,
        prefix: Option<Prefix>,
        document: &Document,
    ) -> Element {
        Element::new_inherited_with_state(
            ElementState::empty(),
            local_name,
            namespace,
            prefix,
            document,
        )
    }

    pub fn new_inherited_with_state(
        state: ElementState,
        local_name: LocalName,
        namespace: Namespace,
        prefix: Option<Prefix>,
        document: &Document,
    ) -> Element {
        Element {
            node: Node::new_inherited(document),
            local_name: local_name,
            tag_name: TagName::new(),
            namespace: namespace,
            prefix: DomRefCell::new(prefix),
            attrs: DomRefCell::new(vec![]),
            id_attribute: DomRefCell::new(None),
            is: DomRefCell::new(None),
            style_attribute: DomRefCell::new(None),
            attr_list: Default::default(),
            class_list: Default::default(),
            state: Cell::new(state),
            selector_flags: Cell::new(ElementSelectorFlags::empty()),
            custom_element_reaction_queue: Default::default(),
            custom_element_definition: Default::default(),
            custom_element_state: Cell::new(CustomElementState::Uncustomized),
        }
    }

    pub fn new(
        local_name: LocalName,
        namespace: Namespace,
        prefix: Option<Prefix>,
        document: &Document,
    ) -> DomRoot<Element> {
        Node::reflect_node(
            Box::new(Element::new_inherited(
                local_name, namespace, prefix, document,
            )),
            document,
            ElementBinding::Wrap,
        )
    }

    pub fn restyle(&self, damage: NodeDamage) {
        let doc = self.node.owner_doc();
        let mut restyle = doc.ensure_pending_restyle(self);

        // FIXME(bholley): I think we should probably only do this for
        // NodeStyleDamaged, but I'm preserving existing behavior.
        restyle.hint.insert(RestyleHint::RESTYLE_SELF);

        if damage == NodeDamage::OtherNodeDamage {
            restyle.damage = RestyleDamage::rebuild_and_reflow();
        }
    }

    pub fn set_is(&self, is: LocalName) {
        *self.is.borrow_mut() = Some(is);
    }

    pub fn get_is(&self) -> Option<LocalName> {
        self.is.borrow().clone()
    }

    pub fn set_custom_element_state(&self, state: CustomElementState) {
        self.custom_element_state.set(state);
    }

    pub fn get_custom_element_state(&self) -> CustomElementState {
        self.custom_element_state.get()
    }

    pub fn set_custom_element_definition(&self, definition: Rc<CustomElementDefinition>) {
        *self.custom_element_definition.borrow_mut() = Some(definition);
    }

    pub fn get_custom_element_definition(&self) -> Option<Rc<CustomElementDefinition>> {
        (*self.custom_element_definition.borrow()).clone()
    }

    pub fn push_callback_reaction(&self, function: Rc<Function>, args: Box<[Heap<JSVal>]>) {
        self.custom_element_reaction_queue
            .borrow_mut()
            .push(CustomElementReaction::Callback(function, args));
    }

    pub fn push_upgrade_reaction(&self, definition: Rc<CustomElementDefinition>) {
        self.custom_element_reaction_queue
            .borrow_mut()
            .push(CustomElementReaction::Upgrade(definition));
    }

    pub fn clear_reaction_queue(&self) {
        self.custom_element_reaction_queue.borrow_mut().clear();
    }

    pub fn invoke_reactions(&self) {
        // TODO: This is not spec compliant, as this will allow some reactions to be processed
        // after clear_reaction_queue has been called.
        rooted_vec!(let mut reactions);
        while !self.custom_element_reaction_queue.borrow().is_empty() {
            mem::swap(
                &mut *reactions,
                &mut *self.custom_element_reaction_queue.borrow_mut(),
            );
            for reaction in reactions.iter() {
                reaction.invoke(self);
            }
            reactions.clear();
        }
    }

    /// style will be `None` for elements in a `display: none` subtree. otherwise, the element has a
    /// layout box iff it doesn't have `display: none`.
    pub fn style(&self) -> Option<Arc<ComputedValues>> {
        window_from_node(self).style_query(self.upcast::<Node>().to_trusted_node_address())
    }

    // https://drafts.csswg.org/cssom-view/#css-layout-box
    pub fn has_css_layout_box(&self) -> bool {
        self.style()
            .map_or(false, |s| !s.get_box().clone_display().is_none())
    }

    // https://drafts.csswg.org/cssom-view/#potentially-scrollable
    fn potentially_scrollable(&self) -> bool {
        self.has_css_layout_box() && !self.has_any_visible_overflow()
    }

    // https://drafts.csswg.org/cssom-view/#scrolling-box
    fn has_scrolling_box(&self) -> bool {
        // TODO: scrolling mechanism, such as scrollbar (We don't have scrollbar yet)
        //       self.has_scrolling_mechanism()
        self.has_any_hidden_overflow()
    }

    fn has_overflow(&self) -> bool {
        self.ScrollHeight() > self.ClientHeight() || self.ScrollWidth() > self.ClientWidth()
    }

    // TODO: Once #19183 is closed (overflow-x/y types moved out of mako), then we could implement
    //       a more generic `fn has_some_overflow(&self, overflow: Overflow)` rather than have
    //       these two `has_any_{visible,hidden}_overflow` methods which are very structurally
    //       similar.

    /// Computed value of overflow-x or overflow-y is "visible"
    fn has_any_visible_overflow(&self) -> bool {
        self.style().map_or(false, |s| {
            let box_ = s.get_box();

            box_.clone_overflow_x() == overflow_x::computed_value::T::Visible ||
                box_.clone_overflow_y() == overflow_y::computed_value::T::Visible
        })
    }

    /// Computed value of overflow-x or overflow-y is "hidden"
    fn has_any_hidden_overflow(&self) -> bool {
        self.style().map_or(false, |s| {
            let box_ = s.get_box();

            box_.clone_overflow_x() == overflow_x::computed_value::T::Hidden ||
                box_.clone_overflow_y() == overflow_y::computed_value::T::Hidden
        })
    }
}

#[allow(unsafe_code)]
pub trait RawLayoutElementHelpers {
    unsafe fn get_attr_for_layout<'a>(
        &'a self,
        namespace: &Namespace,
        name: &LocalName,
    ) -> Option<&'a AttrValue>;
    unsafe fn get_attr_val_for_layout<'a>(
        &'a self,
        namespace: &Namespace,
        name: &LocalName,
    ) -> Option<&'a str>;
    unsafe fn get_attr_vals_for_layout<'a>(&'a self, name: &LocalName) -> Vec<&'a AttrValue>;
}

#[inline]
#[allow(unsafe_code)]
pub unsafe fn get_attr_for_layout<'a>(
    elem: &'a Element,
    namespace: &Namespace,
    name: &LocalName,
) -> Option<LayoutDom<Attr>> {
    // cast to point to T in RefCell<T> directly
    let attrs = elem.attrs.borrow_for_layout();
    attrs
        .iter()
        .find(|attr| {
            let attr = attr.to_layout();
            *name == attr.local_name_atom_forever() && (*attr.unsafe_get()).namespace() == namespace
        }).map(|attr| attr.to_layout())
}

#[allow(unsafe_code)]
impl RawLayoutElementHelpers for Element {
    #[inline]
    unsafe fn get_attr_for_layout<'a>(
        &'a self,
        namespace: &Namespace,
        name: &LocalName,
    ) -> Option<&'a AttrValue> {
        get_attr_for_layout(self, namespace, name).map(|attr| attr.value_forever())
    }

    #[inline]
    unsafe fn get_attr_val_for_layout<'a>(
        &'a self,
        namespace: &Namespace,
        name: &LocalName,
    ) -> Option<&'a str> {
        get_attr_for_layout(self, namespace, name).map(|attr| attr.value_ref_forever())
    }

    #[inline]
    unsafe fn get_attr_vals_for_layout<'a>(&'a self, name: &LocalName) -> Vec<&'a AttrValue> {
        let attrs = self.attrs.borrow_for_layout();
        attrs
            .iter()
            .filter_map(|attr| {
                let attr = attr.to_layout();
                if *name == attr.local_name_atom_forever() {
                    Some(attr.value_forever())
                } else {
                    None
                }
            }).collect()
    }
}

pub trait LayoutElementHelpers {
    #[allow(unsafe_code)]
    unsafe fn has_class_for_layout(&self, name: &Atom, case_sensitivity: CaseSensitivity) -> bool;
    #[allow(unsafe_code)]
    unsafe fn get_classes_for_layout(&self) -> Option<&'static [Atom]>;

    #[allow(unsafe_code)]
    unsafe fn synthesize_presentational_hints_for_legacy_attributes<V>(&self, _: &mut V)
    where
        V: Push<ApplicableDeclarationBlock>;
    #[allow(unsafe_code)]
    unsafe fn get_colspan(self) -> u32;
    #[allow(unsafe_code)]
    unsafe fn get_rowspan(self) -> u32;
    #[allow(unsafe_code)]
    unsafe fn is_html_element(&self) -> bool;
    fn id_attribute(&self) -> *const Option<Atom>;
    fn style_attribute(&self) -> *const Option<Arc<Locked<PropertyDeclarationBlock>>>;
    fn local_name(&self) -> &LocalName;
    fn namespace(&self) -> &Namespace;
    fn get_lang_for_layout(&self) -> String;
    fn get_checked_state_for_layout(&self) -> bool;
    fn get_indeterminate_state_for_layout(&self) -> bool;
    fn get_state_for_layout(&self) -> ElementState;
    fn insert_selector_flags(&self, flags: ElementSelectorFlags);
    fn has_selector_flags(&self, flags: ElementSelectorFlags) -> bool;
}

impl LayoutElementHelpers for LayoutDom<Element> {
    #[allow(unsafe_code)]
    #[inline]
    unsafe fn has_class_for_layout(&self, name: &Atom, case_sensitivity: CaseSensitivity) -> bool {
        get_attr_for_layout(&*self.unsafe_get(), &ns!(), &local_name!("class")).map_or(
            false,
            |attr| {
                attr.value_tokens_forever()
                    .unwrap()
                    .iter()
                    .any(|atom| case_sensitivity.eq_atom(atom, name))
            },
        )
    }

    #[allow(unsafe_code)]
    #[inline]
    unsafe fn get_classes_for_layout(&self) -> Option<&'static [Atom]> {
        get_attr_for_layout(&*self.unsafe_get(), &ns!(), &local_name!("class"))
            .map(|attr| attr.value_tokens_forever().unwrap())
    }

    #[allow(unsafe_code)]
    unsafe fn synthesize_presentational_hints_for_legacy_attributes<V>(&self, hints: &mut V)
    where
        V: Push<ApplicableDeclarationBlock>,
    {
        // FIXME(emilio): Just a single PDB should be enough.
        #[inline]
        fn from_declaration(
            shared_lock: &SharedRwLock,
            declaration: PropertyDeclaration,
        ) -> ApplicableDeclarationBlock {
            ApplicableDeclarationBlock::from_declarations(
                Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
                    declaration,
                    Importance::Normal,
                ))),
                CascadeLevel::PresHints,
            )
        }

        let document = self.upcast::<Node>().owner_doc_for_layout();
        let shared_lock = document.style_shared_lock();

        let bgcolor = if let Some(this) = self.downcast::<HTMLBodyElement>() {
            this.get_background_color()
        } else if let Some(this) = self.downcast::<HTMLTableElement>() {
            this.get_background_color()
        } else if let Some(this) = self.downcast::<HTMLTableCellElement>() {
            this.get_background_color()
        } else if let Some(this) = self.downcast::<HTMLTableRowElement>() {
            this.get_background_color()
        } else if let Some(this) = self.downcast::<HTMLTableSectionElement>() {
            this.get_background_color()
        } else {
            None
        };

        if let Some(color) = bgcolor {
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::BackgroundColor(color.into()),
            ));
        }

        let background = if let Some(this) = self.downcast::<HTMLBodyElement>() {
            this.get_background()
        } else {
            None
        };

        if let Some(url) = background {
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::BackgroundImage(background_image::SpecifiedValue(vec![
                    Either::Second(specified::Image::for_cascade(url.into())),
                ])),
            ));
        }

        let color = if let Some(this) = self.downcast::<HTMLFontElement>() {
            this.get_color()
        } else if let Some(this) = self.downcast::<HTMLBodyElement>() {
            // https://html.spec.whatwg.org/multipage/#the-page:the-body-element-20
            this.get_color()
        } else if let Some(this) = self.downcast::<HTMLHRElement>() {
            // https://html.spec.whatwg.org/multipage/#the-hr-element-2:presentational-hints-5
            this.get_color()
        } else {
            None
        };

        if let Some(color) = color {
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::Color(longhands::color::SpecifiedValue(color.into())),
            ));
        }

        let font_family = if let Some(this) = self.downcast::<HTMLFontElement>() {
            this.get_face()
        } else {
            None
        };

        if let Some(font_family) = font_family {
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::FontFamily(font_family::SpecifiedValue::Values(
                    computed::font::FontFamilyList::new(Box::new([
                        computed::font::SingleFontFamily::from_atom(font_family),
                    ])),
                )),
            ));
        }

        let font_size = self
            .downcast::<HTMLFontElement>()
            .and_then(|this| this.get_size());

        if let Some(font_size) = font_size {
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::FontSize(font_size::SpecifiedValue::from_html_size(
                    font_size as u8,
                )),
            ))
        }

        let cellspacing = if let Some(this) = self.downcast::<HTMLTableElement>() {
            this.get_cellspacing()
        } else {
            None
        };

        if let Some(cellspacing) = cellspacing {
            let width_value = specified::Length::from_px(cellspacing as f32);
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::BorderSpacing(Box::new(border_spacing::SpecifiedValue::new(
                    width_value.clone().into(),
                    width_value.into(),
                ))),
            ));
        }

        let size = if let Some(this) = self.downcast::<HTMLInputElement>() {
            // FIXME(pcwalton): More use of atoms, please!
            match (*self.unsafe_get()).get_attr_val_for_layout(&ns!(), &local_name!("type")) {
                // Not text entry widget
                Some("hidden") |
                Some("date") |
                Some("month") |
                Some("week") |
                Some("time") |
                Some("datetime-local") |
                Some("number") |
                Some("range") |
                Some("color") |
                Some("checkbox") |
                Some("radio") |
                Some("file") |
                Some("submit") |
                Some("image") |
                Some("reset") |
                Some("button") => None,
                // Others
                _ => match this.size_for_layout() {
                    0 => None,
                    s => Some(s as i32),
                },
            }
        } else {
            None
        };

        if let Some(size) = size {
            let value =
                specified::NoCalcLength::ServoCharacterWidth(specified::CharacterWidth(size));
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::Width(specified::LengthOrPercentageOrAuto::Length(value)),
            ));
        }

        let width = if let Some(this) = self.downcast::<HTMLIFrameElement>() {
            this.get_width()
        } else if let Some(this) = self.downcast::<HTMLImageElement>() {
            this.get_width()
        } else if let Some(this) = self.downcast::<HTMLTableElement>() {
            this.get_width()
        } else if let Some(this) = self.downcast::<HTMLTableCellElement>() {
            this.get_width()
        } else if let Some(this) = self.downcast::<HTMLHRElement>() {
            // https://html.spec.whatwg.org/multipage/#the-hr-element-2:attr-hr-width
            this.get_width()
        } else if let Some(this) = self.downcast::<HTMLCanvasElement>() {
            this.get_width()
        } else {
            LengthOrPercentageOrAuto::Auto
        };

        // FIXME(emilio): Use from_computed value here and below.
        match width {
            LengthOrPercentageOrAuto::Auto => {},
            LengthOrPercentageOrAuto::Percentage(percentage) => {
                let width_value = specified::LengthOrPercentageOrAuto::Percentage(
                    computed::Percentage(percentage),
                );
                hints.push(from_declaration(
                    shared_lock,
                    PropertyDeclaration::Width(width_value),
                ));
            },
            LengthOrPercentageOrAuto::Length(length) => {
                let width_value =
                    specified::LengthOrPercentageOrAuto::Length(specified::NoCalcLength::Absolute(
                        specified::AbsoluteLength::Px(length.to_f32_px()),
                    ));
                hints.push(from_declaration(
                    shared_lock,
                    PropertyDeclaration::Width(width_value),
                ));
            },
        }

        let height = if let Some(this) = self.downcast::<HTMLIFrameElement>() {
            this.get_height()
        } else if let Some(this) = self.downcast::<HTMLImageElement>() {
            this.get_height()
        } else if let Some(this) = self.downcast::<HTMLCanvasElement>() {
            this.get_height()
        } else {
            LengthOrPercentageOrAuto::Auto
        };

        match height {
            LengthOrPercentageOrAuto::Auto => {},
            LengthOrPercentageOrAuto::Percentage(percentage) => {
                let height_value = specified::LengthOrPercentageOrAuto::Percentage(
                    computed::Percentage(percentage),
                );
                hints.push(from_declaration(
                    shared_lock,
                    PropertyDeclaration::Height(height_value),
                ));
            },
            LengthOrPercentageOrAuto::Length(length) => {
                let height_value =
                    specified::LengthOrPercentageOrAuto::Length(specified::NoCalcLength::Absolute(
                        specified::AbsoluteLength::Px(length.to_f32_px()),
                    ));
                hints.push(from_declaration(
                    shared_lock,
                    PropertyDeclaration::Height(height_value),
                ));
            },
        }

        let cols = if let Some(this) = self.downcast::<HTMLTextAreaElement>() {
            match this.get_cols() {
                0 => None,
                c => Some(c as i32),
            }
        } else {
            None
        };

        if let Some(cols) = cols {
            // TODO(mttr) ServoCharacterWidth uses the size math for <input type="text">, but
            // the math for <textarea> is a little different since we need to take
            // scrollbar size into consideration (but we don't have a scrollbar yet!)
            //
            // https://html.spec.whatwg.org/multipage/#textarea-effective-width
            let value =
                specified::NoCalcLength::ServoCharacterWidth(specified::CharacterWidth(cols));
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::Width(specified::LengthOrPercentageOrAuto::Length(value)),
            ));
        }

        let rows = if let Some(this) = self.downcast::<HTMLTextAreaElement>() {
            match this.get_rows() {
                0 => None,
                r => Some(r as i32),
            }
        } else {
            None
        };

        if let Some(rows) = rows {
            // TODO(mttr) This should take scrollbar size into consideration.
            //
            // https://html.spec.whatwg.org/multipage/#textarea-effective-height
            let value = specified::NoCalcLength::FontRelative(specified::FontRelativeLength::Em(
                rows as CSSFloat,
            ));
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::Height(specified::LengthOrPercentageOrAuto::Length(value)),
            ));
        }

        let border = if let Some(this) = self.downcast::<HTMLTableElement>() {
            this.get_border()
        } else {
            None
        };

        if let Some(border) = border {
            let width_value =
                specified::BorderSideWidth::Length(specified::Length::from_px(border as f32));
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::BorderTopWidth(width_value.clone()),
            ));
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::BorderLeftWidth(width_value.clone()),
            ));
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::BorderBottomWidth(width_value.clone()),
            ));
            hints.push(from_declaration(
                shared_lock,
                PropertyDeclaration::BorderRightWidth(width_value),
            ));
        }
    }

    #[allow(unsafe_code)]
    unsafe fn get_colspan(self) -> u32 {
        if let Some(this) = self.downcast::<HTMLTableCellElement>() {
            this.get_colspan().unwrap_or(1)
        } else {
            // Don't panic since `display` can cause this to be called on arbitrary
            // elements.
            1
        }
    }

    #[allow(unsafe_code)]
    unsafe fn get_rowspan(self) -> u32 {
        if let Some(this) = self.downcast::<HTMLTableCellElement>() {
            this.get_rowspan().unwrap_or(1)
        } else {
            // Don't panic since `display` can cause this to be called on arbitrary
            // elements.
            1
        }
    }

    #[inline]
    #[allow(unsafe_code)]
    unsafe fn is_html_element(&self) -> bool {
        (*self.unsafe_get()).namespace == ns!(html)
    }

    #[allow(unsafe_code)]
    fn id_attribute(&self) -> *const Option<Atom> {
        unsafe { (*self.unsafe_get()).id_attribute.borrow_for_layout() }
    }

    #[allow(unsafe_code)]
    fn style_attribute(&self) -> *const Option<Arc<Locked<PropertyDeclarationBlock>>> {
        unsafe { (*self.unsafe_get()).style_attribute.borrow_for_layout() }
    }

    #[allow(unsafe_code)]
    fn local_name(&self) -> &LocalName {
        unsafe { &(*self.unsafe_get()).local_name }
    }

    #[allow(unsafe_code)]
    fn namespace(&self) -> &Namespace {
        unsafe { &(*self.unsafe_get()).namespace }
    }

    #[allow(unsafe_code)]
    fn get_lang_for_layout(&self) -> String {
        unsafe {
            let mut current_node = Some(self.upcast::<Node>());
            while let Some(node) = current_node {
                current_node = node.parent_node_ref();
                match node.downcast::<Element>().map(|el| el.unsafe_get()) {
                    Some(elem) => {
                        if let Some(attr) =
                            (*elem).get_attr_val_for_layout(&ns!(xml), &local_name!("lang"))
                        {
                            return attr.to_owned();
                        }
                        if let Some(attr) =
                            (*elem).get_attr_val_for_layout(&ns!(), &local_name!("lang"))
                        {
                            return attr.to_owned();
                        }
                    },
                    None => continue,
                }
            }
            // TODO: Check meta tags for a pragma-set default language
            // TODO: Check HTTP Content-Language header
            String::new()
        }
    }

    #[inline]
    #[allow(unsafe_code)]
    fn get_checked_state_for_layout(&self) -> bool {
        // TODO option and menuitem can also have a checked state.
        match self.downcast::<HTMLInputElement>() {
            Some(input) => unsafe { input.checked_state_for_layout() },
            None => false,
        }
    }

    #[inline]
    #[allow(unsafe_code)]
    fn get_indeterminate_state_for_layout(&self) -> bool {
        // TODO progress elements can also be matched with :indeterminate
        match self.downcast::<HTMLInputElement>() {
            Some(input) => unsafe { input.indeterminate_state_for_layout() },
            None => false,
        }
    }

    #[inline]
    #[allow(unsafe_code)]
    fn get_state_for_layout(&self) -> ElementState {
        unsafe { (*self.unsafe_get()).state.get() }
    }

    #[inline]
    #[allow(unsafe_code)]
    fn insert_selector_flags(&self, flags: ElementSelectorFlags) {
        debug_assert!(thread_state::get().is_layout());
        unsafe {
            let f = &(*self.unsafe_get()).selector_flags;
            f.set(f.get() | flags);
        }
    }

    #[inline]
    #[allow(unsafe_code)]
    fn has_selector_flags(&self, flags: ElementSelectorFlags) -> bool {
        unsafe { (*self.unsafe_get()).selector_flags.get().contains(flags) }
    }
}

impl Element {
    pub fn is_html_element(&self) -> bool {
        self.namespace == ns!(html)
    }

    pub fn html_element_in_html_document(&self) -> bool {
        self.is_html_element() && self.upcast::<Node>().is_in_html_doc()
    }

    pub fn local_name(&self) -> &LocalName {
        &self.local_name
    }

    pub fn parsed_name(&self, mut name: DOMString) -> LocalName {
        if self.html_element_in_html_document() {
            name.make_ascii_lowercase();
        }
        LocalName::from(name)
    }

    pub fn namespace(&self) -> &Namespace {
        &self.namespace
    }

    pub fn prefix(&self) -> Ref<Option<Prefix>> {
        self.prefix.borrow()
    }

    pub fn set_prefix(&self, prefix: Option<Prefix>) {
        *self.prefix.borrow_mut() = prefix;
    }

    pub fn attrs(&self) -> Ref<[Dom<Attr>]> {
        Ref::map(self.attrs.borrow(), |attrs| &**attrs)
    }

    // Element branch of https://dom.spec.whatwg.org/#locate-a-namespace
    pub fn locate_namespace(&self, prefix: Option<DOMString>) -> Namespace {
        let prefix = prefix.map(String::from).map(LocalName::from);

        let inclusive_ancestor_elements = self
            .upcast::<Node>()
            .inclusive_ancestors()
            .filter_map(DomRoot::downcast::<Self>);

        // Steps 3-4.
        for element in inclusive_ancestor_elements {
            // Step 1.
            if element.namespace() != &ns!() &&
                element.prefix().as_ref().map(|p| &**p) == prefix.as_ref().map(|p| &**p)
            {
                return element.namespace().clone();
            }

            // Step 2.
            let attr = ref_filter_map(self.attrs(), |attrs| {
                attrs.iter().find(|attr| {
                    if attr.namespace() != &ns!(xmlns) {
                        return false;
                    }
                    match (attr.prefix(), prefix.as_ref()) {
                        (Some(&namespace_prefix!("xmlns")), Some(prefix)) => {
                            attr.local_name() == prefix
                        },
                        (None, None) => attr.local_name() == &local_name!("xmlns"),
                        _ => false,
                    }
                })
            });

            if let Some(attr) = attr {
                return (**attr.value()).into();
            }
        }

        ns!()
    }

    pub fn style_attribute(&self) -> &DomRefCell<Option<Arc<Locked<PropertyDeclarationBlock>>>> {
        &self.style_attribute
    }

    pub fn summarize(&self) -> Vec<AttrInfo> {
        self.attrs
            .borrow()
            .iter()
            .map(|attr| attr.summarize())
            .collect()
    }

    pub fn is_void(&self) -> bool {
        if self.namespace != ns!(html) {
            return false;
        }
        match self.local_name {
            /* List of void elements from
            https://html.spec.whatwg.org/multipage/#html-fragment-serialisation-algorithm */
            local_name!("area") |
            local_name!("base") |
            local_name!("basefont") |
            local_name!("bgsound") |
            local_name!("br") |
            local_name!("col") |
            local_name!("embed") |
            local_name!("frame") |
            local_name!("hr") |
            local_name!("img") |
            local_name!("input") |
            local_name!("keygen") |
            local_name!("link") |
            local_name!("menuitem") |
            local_name!("meta") |
            local_name!("param") |
            local_name!("source") |
            local_name!("track") |
            local_name!("wbr") => true,
            _ => false,
        }
    }

    pub fn serialize(&self, traversal_scope: TraversalScope) -> Fallible<DOMString> {
        let mut writer = vec![];
        match serialize(
            &mut writer,
            &self.upcast::<Node>(),
            SerializeOpts {
                traversal_scope: traversal_scope,
                ..Default::default()
            },
        ) {
            // FIXME(ajeffrey): Directly convert UTF8 to DOMString
            Ok(()) => Ok(DOMString::from(String::from_utf8(writer).unwrap())),
            Err(_) => panic!("Cannot serialize element"),
        }
    }

    pub fn xmlSerialize(&self, traversal_scope: XmlTraversalScope) -> Fallible<DOMString> {
        let mut writer = vec![];
        match xmlSerialize::serialize(
            &mut writer,
            &self.upcast::<Node>(),
            XmlSerializeOpts {
                traversal_scope: traversal_scope,
                ..Default::default()
            },
        ) {
            Ok(()) => Ok(DOMString::from(String::from_utf8(writer).unwrap())),
            Err(_) => panic!("Cannot serialize element"),
        }
    }

    pub fn root_element(&self) -> DomRoot<Element> {
        if self.node.is_in_doc() {
            self.upcast::<Node>()
                .owner_doc()
                .GetDocumentElement()
                .unwrap()
        } else {
            self.upcast::<Node>()
                .inclusive_ancestors()
                .filter_map(DomRoot::downcast)
                .last()
                .expect("We know inclusive_ancestors will return `self` which is an element")
        }
    }

    // https://dom.spec.whatwg.org/#locate-a-namespace-prefix
    pub fn lookup_prefix(&self, namespace: Namespace) -> Option<DOMString> {
        for node in self.upcast::<Node>().inclusive_ancestors() {
            let element = node.downcast::<Element>()?;
            // Step 1.
            if *element.namespace() == namespace {
                if let Some(prefix) = element.GetPrefix() {
                    return Some(prefix);
                }
            }

            // Step 2.
            for attr in element.attrs.borrow().iter() {
                if attr.prefix() == Some(&namespace_prefix!("xmlns")) &&
                    **attr.value() == *namespace
                {
                    return Some(attr.LocalName());
                }
            }
        }
        None
    }

    // Returns the kind of IME control needed for a focusable element, if any.
    pub fn input_method_type(&self) -> Option<InputMethodType> {
        if !self.is_focusable_area() {
            return None;
        }

        if let Some(input) = self.downcast::<HTMLInputElement>() {
            input.input_type().as_ime_type()
        } else if self.is::<HTMLTextAreaElement>() {
            Some(InputMethodType::Text)
        } else {
            // Other focusable elements that are not input fields.
            None
        }
    }

    pub fn is_focusable_area(&self) -> bool {
        if self.is_actually_disabled() {
            return false;
        }
        // TODO: Check whether the element is being rendered (i.e. not hidden).
        let node = self.upcast::<Node>();
        if node.get_flag(NodeFlags::SEQUENTIALLY_FOCUSABLE) {
            return true;
        }
        // https://html.spec.whatwg.org/multipage/#specially-focusable
        match node.type_id() {
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLAnchorElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLInputElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLSelectElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLTextAreaElement,
            )) => true,
            _ => false,
        }
    }

    pub fn is_actually_disabled(&self) -> bool {
        let node = self.upcast::<Node>();
        match node.type_id() {
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLButtonElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLInputElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLSelectElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLTextAreaElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLOptionElement,
            )) => self.disabled_state(),
            // TODO:
            // an optgroup element that has a disabled attribute
            // a menuitem element that has a disabled attribute
            // a fieldset element that is a disabled fieldset
            _ => false,
        }
    }

    pub fn push_new_attribute(
        &self,
        local_name: LocalName,
        value: AttrValue,
        name: LocalName,
        namespace: Namespace,
        prefix: Option<Prefix>,
    ) {
        let window = window_from_node(self);
        let attr = Attr::new(
            &window,
            local_name,
            value,
            name,
            namespace,
            prefix,
            Some(self),
        );
        self.push_attribute(&attr);
    }

    pub fn push_attribute(&self, attr: &Attr) {
        let name = attr.local_name().clone();
        let namespace = attr.namespace().clone();
        let mutation = Mutation::Attribute {
            name: name.clone(),
            namespace: namespace.clone(),
            old_value: None,
        };

        MutationObserver::queue_a_mutation_record(&self.node, mutation);

        if self.get_custom_element_definition().is_some() {
            let value = DOMString::from(&**attr.value());
            let reaction = CallbackReaction::AttributeChanged(name, None, Some(value), namespace);
            ScriptThread::enqueue_callback_reaction(self, reaction, None);
        }

        assert!(attr.GetOwnerElement().r() == Some(self));
        self.will_mutate_attr(attr);
        self.attrs.borrow_mut().push(Dom::from_ref(attr));
        if attr.namespace() == &ns!() {
            vtable_for(self.upcast()).attribute_mutated(attr, AttributeMutation::Set(None));
        }
    }

    pub fn get_attribute(
        &self,
        namespace: &Namespace,
        local_name: &LocalName,
    ) -> Option<DomRoot<Attr>> {
        self.attrs
            .borrow()
            .iter()
            .find(|attr| attr.local_name() == local_name && attr.namespace() == namespace)
            .map(|js| DomRoot::from_ref(&**js))
    }

    // https://dom.spec.whatwg.org/#concept-element-attributes-get-by-name
    pub fn get_attribute_by_name(&self, name: DOMString) -> Option<DomRoot<Attr>> {
        let name = &self.parsed_name(name);
        self.attrs
            .borrow()
            .iter()
            .find(|a| a.name() == name)
            .map(|js| DomRoot::from_ref(&**js))
    }

    pub fn set_attribute_from_parser(
        &self,
        qname: QualName,
        value: DOMString,
        prefix: Option<Prefix>,
    ) {
        // Don't set if the attribute already exists, so we can handle add_attrs_if_missing
        if self
            .attrs
            .borrow()
            .iter()
            .any(|a| *a.local_name() == qname.local && *a.namespace() == qname.ns)
        {
            return;
        }

        let name = match prefix {
            None => qname.local.clone(),
            Some(ref prefix) => {
                let name = format!("{}:{}", &**prefix, &*qname.local);
                LocalName::from(name)
            },
        };
        let value = self.parse_attribute(&qname.ns, &qname.local, value);
        self.push_new_attribute(qname.local, value, name, qname.ns, prefix);
    }

    pub fn set_attribute(&self, name: &LocalName, value: AttrValue) {
        assert!(name == &name.to_ascii_lowercase());
        assert!(!name.contains(":"));

        self.set_first_matching_attribute(name.clone(), value, name.clone(), ns!(), None, |attr| {
            attr.local_name() == name
        });
    }

    // https://html.spec.whatwg.org/multipage/#attr-data-*
    pub fn set_custom_attribute(&self, name: DOMString, value: DOMString) -> ErrorResult {
        // Step 1.
        if let InvalidXMLName = xml_name_type(&name) {
            return Err(Error::InvalidCharacter);
        }

        // Steps 2-5.
        let name = LocalName::from(name);
        let value = self.parse_attribute(&ns!(), &name, value);
        self.set_first_matching_attribute(name.clone(), value, name.clone(), ns!(), None, |attr| {
            *attr.name() == name && *attr.namespace() == ns!()
        });
        Ok(())
    }

    fn set_first_matching_attribute<F>(
        &self,
        local_name: LocalName,
        value: AttrValue,
        name: LocalName,
        namespace: Namespace,
        prefix: Option<Prefix>,
        find: F,
    ) where
        F: Fn(&Attr) -> bool,
    {
        let attr = self
            .attrs
            .borrow()
            .iter()
            .find(|attr| find(&attr))
            .map(|js| DomRoot::from_ref(&**js));
        if let Some(attr) = attr {
            attr.set_value(value, self);
        } else {
            self.push_new_attribute(local_name, value, name, namespace, prefix);
        };
    }

    pub fn parse_attribute(
        &self,
        namespace: &Namespace,
        local_name: &LocalName,
        value: DOMString,
    ) -> AttrValue {
        if *namespace == ns!() {
            vtable_for(self.upcast()).parse_plain_attribute(local_name, value)
        } else {
            AttrValue::String(value.into())
        }
    }

    pub fn remove_attribute(
        &self,
        namespace: &Namespace,
        local_name: &LocalName,
    ) -> Option<DomRoot<Attr>> {
        self.remove_first_matching_attribute(|attr| {
            attr.namespace() == namespace && attr.local_name() == local_name
        })
    }

    pub fn remove_attribute_by_name(&self, name: &LocalName) -> Option<DomRoot<Attr>> {
        self.remove_first_matching_attribute(|attr| attr.name() == name)
    }

    fn remove_first_matching_attribute<F>(&self, find: F) -> Option<DomRoot<Attr>>
    where
        F: Fn(&Attr) -> bool,
    {
        let idx = self.attrs.borrow().iter().position(|attr| find(&attr));
        idx.map(|idx| {
            let attr = DomRoot::from_ref(&*(*self.attrs.borrow())[idx]);
            self.will_mutate_attr(&attr);

            let name = attr.local_name().clone();
            let namespace = attr.namespace().clone();
            let old_value = DOMString::from(&**attr.value());
            let mutation = Mutation::Attribute {
                name: name.clone(),
                namespace: namespace.clone(),
                old_value: Some(old_value.clone()),
            };

            MutationObserver::queue_a_mutation_record(&self.node, mutation);

            let reaction =
                CallbackReaction::AttributeChanged(name, Some(old_value), None, namespace);
            ScriptThread::enqueue_callback_reaction(self, reaction, None);

            self.attrs.borrow_mut().remove(idx);
            attr.set_owner(None);
            if attr.namespace() == &ns!() {
                vtable_for(self.upcast()).attribute_mutated(&attr, AttributeMutation::Removed);
            }
            attr
        })
    }

    pub fn has_class(&self, name: &Atom, case_sensitivity: CaseSensitivity) -> bool {
        self.get_attribute(&ns!(), &local_name!("class"))
            .map_or(false, |attr| {
                attr.value()
                    .as_tokens()
                    .iter()
                    .any(|atom| case_sensitivity.eq_atom(name, atom))
            })
    }

    pub fn set_atomic_attribute(&self, local_name: &LocalName, value: DOMString) {
        assert!(*local_name == local_name.to_ascii_lowercase());
        let value = AttrValue::from_atomic(value.into());
        self.set_attribute(local_name, value);
    }

    pub fn has_attribute(&self, local_name: &LocalName) -> bool {
        assert!(local_name.bytes().all(|b| b.to_ascii_lowercase() == b));
        self.attrs
            .borrow()
            .iter()
            .any(|attr| attr.local_name() == local_name && attr.namespace() == &ns!())
    }

    pub fn set_bool_attribute(&self, local_name: &LocalName, value: bool) {
        if self.has_attribute(local_name) == value {
            return;
        }
        if value {
            self.set_string_attribute(local_name, DOMString::new());
        } else {
            self.remove_attribute(&ns!(), local_name);
        }
    }

    pub fn get_url_attribute(&self, local_name: &LocalName) -> DOMString {
        assert!(*local_name == local_name.to_ascii_lowercase());
        let attr = match self.get_attribute(&ns!(), local_name) {
            Some(attr) => attr,
            None => return DOMString::new(),
        };
        let value = &**attr.value();
        // XXXManishearth this doesn't handle `javascript:` urls properly
        let base = document_from_node(self).base_url();
        let value = base
            .join(value)
            .map(|parsed| parsed.into_string())
            .unwrap_or_else(|_| value.to_owned());
        DOMString::from(value)
    }

    pub fn get_string_attribute(&self, local_name: &LocalName) -> DOMString {
        match self.get_attribute(&ns!(), local_name) {
            Some(x) => x.Value(),
            None => DOMString::new(),
        }
    }

    pub fn set_string_attribute(&self, local_name: &LocalName, value: DOMString) {
        assert!(*local_name == local_name.to_ascii_lowercase());
        self.set_attribute(local_name, AttrValue::String(value.into()));
    }

    pub fn get_tokenlist_attribute(&self, local_name: &LocalName) -> Vec<Atom> {
        self.get_attribute(&ns!(), local_name)
            .map(|attr| attr.value().as_tokens().to_vec())
            .unwrap_or(vec![])
    }

    pub fn set_tokenlist_attribute(&self, local_name: &LocalName, value: DOMString) {
        assert!(*local_name == local_name.to_ascii_lowercase());
        self.set_attribute(
            local_name,
            AttrValue::from_serialized_tokenlist(value.into()),
        );
    }

    pub fn set_atomic_tokenlist_attribute(&self, local_name: &LocalName, tokens: Vec<Atom>) {
        assert!(*local_name == local_name.to_ascii_lowercase());
        self.set_attribute(local_name, AttrValue::from_atomic_tokens(tokens));
    }

    pub fn get_int_attribute(&self, local_name: &LocalName, default: i32) -> i32 {
        // TODO: Is this assert necessary?
        assert!(
            local_name
                .chars()
                .all(|ch| !ch.is_ascii() || ch.to_ascii_lowercase() == ch)
        );
        let attribute = self.get_attribute(&ns!(), local_name);

        match attribute {
            Some(ref attribute) => match *attribute.value() {
                AttrValue::Int(_, value) => value,
                _ => panic!(
                    "Expected an AttrValue::Int: \
                     implement parse_plain_attribute"
                ),
            },
            None => default,
        }
    }

    pub fn set_int_attribute(&self, local_name: &LocalName, value: i32) {
        assert!(*local_name == local_name.to_ascii_lowercase());
        self.set_attribute(local_name, AttrValue::Int(value.to_string(), value));
    }

    pub fn get_uint_attribute(&self, local_name: &LocalName, default: u32) -> u32 {
        assert!(
            local_name
                .chars()
                .all(|ch| !ch.is_ascii() || ch.to_ascii_lowercase() == ch)
        );
        let attribute = self.get_attribute(&ns!(), local_name);
        match attribute {
            Some(ref attribute) => match *attribute.value() {
                AttrValue::UInt(_, value) => value,
                _ => panic!("Expected an AttrValue::UInt: implement parse_plain_attribute"),
            },
            None => default,
        }
    }
    pub fn set_uint_attribute(&self, local_name: &LocalName, value: u32) {
        assert!(*local_name == local_name.to_ascii_lowercase());
        self.set_attribute(local_name, AttrValue::UInt(value.to_string(), value));
    }

    pub fn will_mutate_attr(&self, attr: &Attr) {
        let node = self.upcast::<Node>();
        node.owner_doc().element_attr_will_change(self, attr);
    }

    // https://dom.spec.whatwg.org/#insert-adjacent
    pub fn insert_adjacent(
        &self,
        where_: AdjacentPosition,
        node: &Node,
    ) -> Fallible<Option<DomRoot<Node>>> {
        let self_node = self.upcast::<Node>();
        match where_ {
            AdjacentPosition::BeforeBegin => {
                if let Some(parent) = self_node.GetParentNode() {
                    Node::pre_insert(node, &parent, Some(self_node)).map(Some)
                } else {
                    Ok(None)
                }
            },
            AdjacentPosition::AfterBegin => {
                Node::pre_insert(node, &self_node, self_node.GetFirstChild().r()).map(Some)
            },
            AdjacentPosition::BeforeEnd => Node::pre_insert(node, &self_node, None).map(Some),
            AdjacentPosition::AfterEnd => {
                if let Some(parent) = self_node.GetParentNode() {
                    Node::pre_insert(node, &parent, self_node.GetNextSibling().r()).map(Some)
                } else {
                    Ok(None)
                }
            },
        }
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scroll
    pub fn scroll(&self, x_: f64, y_: f64, behavior: ScrollBehavior) {
        // Step 1.2 or 2.3
        let x = if x_.is_finite() { x_ } else { 0.0f64 };
        let y = if y_.is_finite() { y_ } else { 0.0f64 };

        let node = self.upcast::<Node>();

        // Step 3
        let doc = node.owner_doc();

        // Step 4
        if !doc.is_fully_active() {
            return;
        }

        // Step 5
        let win = match doc.GetDefaultView() {
            None => return,
            Some(win) => win,
        };

        // Step 7
        if *self.root_element() == *self {
            if doc.quirks_mode() != QuirksMode::Quirks {
                win.scroll(x, y, behavior);
            }

            return;
        }

        // Step 9
        if doc.GetBody().r() == self.downcast::<HTMLElement>() &&
            doc.quirks_mode() == QuirksMode::Quirks &&
            !self.potentially_scrollable()
        {
            win.scroll(x, y, behavior);
            return;
        }

        // Step 10
        if !self.has_css_layout_box() || !self.has_scrolling_box() || !self.has_overflow() {
            return;
        }

        // Step 11
        win.scroll_node(node, x, y, behavior);
    }

    // https://w3c.github.io/DOM-Parsing/#parsing
    pub fn parse_fragment(&self, markup: DOMString) -> Fallible<DomRoot<DocumentFragment>> {
        // Steps 1-2.
        let context_document = document_from_node(self);
        // TODO(#11995): XML case.
        let new_children = ServoParser::parse_html_fragment(self, markup);
        // Step 3.
        let fragment = DocumentFragment::new(&context_document);
        // Step 4.
        for child in new_children {
            fragment.upcast::<Node>().AppendChild(&child).unwrap();
        }
        // Step 5.
        Ok(fragment)
    }

    pub fn fragment_parsing_context(owner_doc: &Document, element: Option<&Self>) -> DomRoot<Self> {
        match element {
            Some(elem)
                if elem.local_name() != &local_name!("html") ||
                    !elem.html_element_in_html_document() =>
            {
                DomRoot::from_ref(elem)
            },
            _ => DomRoot::upcast(HTMLBodyElement::new(local_name!("body"), None, owner_doc)),
        }
    }

    // https://fullscreen.spec.whatwg.org/#fullscreen-element-ready-check
    pub fn fullscreen_element_ready_check(&self) -> bool {
        if !self.is_connected() {
            return false;
        }
        let document = document_from_node(self);
        document.get_allow_fullscreen()
    }

    // https://html.spec.whatwg.org/multipage/#home-subtree
    pub fn is_in_same_home_subtree<T>(&self, other: &T) -> bool
    where
        T: DerivedFrom<Element> + DomObject,
    {
        let other = other.upcast::<Element>();
        self.root_element() == other.root_element()
    }
}

impl ElementMethods for Element {
    // https://dom.spec.whatwg.org/#dom-element-namespaceuri
    fn GetNamespaceURI(&self) -> Option<DOMString> {
        Node::namespace_to_string(self.namespace.clone())
    }

    // https://dom.spec.whatwg.org/#dom-element-localname
    fn LocalName(&self) -> DOMString {
        // FIXME(ajeffrey): Convert directly from LocalName to DOMString
        DOMString::from(&*self.local_name)
    }

    // https://dom.spec.whatwg.org/#dom-element-prefix
    fn GetPrefix(&self) -> Option<DOMString> {
        self.prefix.borrow().as_ref().map(|p| DOMString::from(&**p))
    }

    // https://dom.spec.whatwg.org/#dom-element-tagname
    fn TagName(&self) -> DOMString {
        let name = self.tag_name.or_init(|| {
            let qualified_name = match *self.prefix.borrow() {
                Some(ref prefix) => Cow::Owned(format!("{}:{}", &**prefix, &*self.local_name)),
                None => Cow::Borrowed(&*self.local_name),
            };
            if self.html_element_in_html_document() {
                LocalName::from(qualified_name.to_ascii_uppercase())
            } else {
                LocalName::from(qualified_name)
            }
        });
        DOMString::from(&*name)
    }

    // https://dom.spec.whatwg.org/#dom-element-id
    fn Id(&self) -> DOMString {
        self.get_string_attribute(&local_name!("id"))
    }

    // https://dom.spec.whatwg.org/#dom-element-id
    fn SetId(&self, id: DOMString) {
        self.set_atomic_attribute(&local_name!("id"), id);
    }

    // https://dom.spec.whatwg.org/#dom-element-classname
    fn ClassName(&self) -> DOMString {
        self.get_string_attribute(&local_name!("class"))
    }

    // https://dom.spec.whatwg.org/#dom-element-classname
    fn SetClassName(&self, class: DOMString) {
        self.set_tokenlist_attribute(&local_name!("class"), class);
    }

    // https://dom.spec.whatwg.org/#dom-element-classlist
    fn ClassList(&self) -> DomRoot<DOMTokenList> {
        self.class_list
            .or_init(|| DOMTokenList::new(self, &local_name!("class")))
    }

    // https://dom.spec.whatwg.org/#dom-element-attributes
    fn Attributes(&self) -> DomRoot<NamedNodeMap> {
        self.attr_list
            .or_init(|| NamedNodeMap::new(&window_from_node(self), self))
    }

    // https://dom.spec.whatwg.org/#dom-element-hasattributes
    fn HasAttributes(&self) -> bool {
        !self.attrs.borrow().is_empty()
    }

    // https://dom.spec.whatwg.org/#dom-element-getattributenames
    fn GetAttributeNames(&self) -> Vec<DOMString> {
        self.attrs.borrow().iter().map(|attr| attr.Name()).collect()
    }

    // https://dom.spec.whatwg.org/#dom-element-getattribute
    fn GetAttribute(&self, name: DOMString) -> Option<DOMString> {
        self.GetAttributeNode(name).map(|s| s.Value())
    }

    // https://dom.spec.whatwg.org/#dom-element-getattributens
    fn GetAttributeNS(
        &self,
        namespace: Option<DOMString>,
        local_name: DOMString,
    ) -> Option<DOMString> {
        self.GetAttributeNodeNS(namespace, local_name)
            .map(|attr| attr.Value())
    }

    // https://dom.spec.whatwg.org/#dom-element-getattributenode
    fn GetAttributeNode(&self, name: DOMString) -> Option<DomRoot<Attr>> {
        self.get_attribute_by_name(name)
    }

    // https://dom.spec.whatwg.org/#dom-element-getattributenodens
    fn GetAttributeNodeNS(
        &self,
        namespace: Option<DOMString>,
        local_name: DOMString,
    ) -> Option<DomRoot<Attr>> {
        let namespace = &namespace_from_domstring(namespace);
        self.get_attribute(namespace, &LocalName::from(local_name))
    }

    // https://dom.spec.whatwg.org/#dom-element-toggleattribute
    fn ToggleAttribute(&self, name: DOMString, force: Option<bool>) -> Fallible<bool> {
        // Step 1.
        if xml_name_type(&name) == InvalidXMLName {
            return Err(Error::InvalidCharacter);
        }

        // Step 3.
        let attribute = self.GetAttribute(name.clone());

        // Step 2.
        let name = self.parsed_name(name);
        match attribute {
            // Step 4
            None => match force {
                // Step 4.1.
                None | Some(true) => {
                    self.set_first_matching_attribute(
                        name.clone(),
                        AttrValue::String(String::new()),
                        name.clone(),
                        ns!(),
                        None,
                        |attr| *attr.name() == name,
                    );
                    Ok(true)
                },
                // Step 4.2.
                Some(false) => Ok(false),
            },
            Some(_index) => match force {
                // Step 5.
                None | Some(false) => {
                    self.remove_attribute_by_name(&name);
                    Ok(false)
                },
                // Step 6.
                Some(true) => Ok(true),
            },
        }
    }

    // https://dom.spec.whatwg.org/#dom-element-setattribute
    fn SetAttribute(&self, name: DOMString, value: DOMString) -> ErrorResult {
        // Step 1.
        if xml_name_type(&name) == InvalidXMLName {
            return Err(Error::InvalidCharacter);
        }

        // Step 2.
        let name = self.parsed_name(name);

        // Step 3-5.
        let value = self.parse_attribute(&ns!(), &name, value);
        self.set_first_matching_attribute(name.clone(), value, name.clone(), ns!(), None, |attr| {
            *attr.name() == name
        });
        Ok(())
    }

    // https://dom.spec.whatwg.org/#dom-element-setattributens
    fn SetAttributeNS(
        &self,
        namespace: Option<DOMString>,
        qualified_name: DOMString,
        value: DOMString,
    ) -> ErrorResult {
        let (namespace, prefix, local_name) = validate_and_extract(namespace, &qualified_name)?;
        let qualified_name = LocalName::from(qualified_name);
        let value = self.parse_attribute(&namespace, &local_name, value);
        self.set_first_matching_attribute(
            local_name.clone(),
            value,
            qualified_name,
            namespace.clone(),
            prefix,
            |attr| *attr.local_name() == local_name && *attr.namespace() == namespace,
        );
        Ok(())
    }

    // https://dom.spec.whatwg.org/#dom-element-setattributenode
    fn SetAttributeNode(&self, attr: &Attr) -> Fallible<Option<DomRoot<Attr>>> {
        // Step 1.
        if let Some(owner) = attr.GetOwnerElement() {
            if &*owner != self {
                return Err(Error::InUseAttribute);
            }
        }

        let vtable = vtable_for(self.upcast());

        // This ensures that the attribute is of the expected kind for this
        // specific element. This is inefficient and should probably be done
        // differently.
        attr.swap_value(&mut vtable.parse_plain_attribute(attr.local_name(), attr.Value()));

        // Step 2.
        let position = self.attrs.borrow().iter().position(|old_attr| {
            attr.namespace() == old_attr.namespace() && attr.local_name() == old_attr.local_name()
        });

        if let Some(position) = position {
            let old_attr = DomRoot::from_ref(&*self.attrs.borrow()[position]);

            // Step 3.
            if &*old_attr == attr {
                return Ok(Some(DomRoot::from_ref(attr)));
            }

            // Step 4.
            if self.get_custom_element_definition().is_some() {
                let old_name = old_attr.local_name().clone();
                let old_value = DOMString::from(&**old_attr.value());
                let new_value = DOMString::from(&**attr.value());
                let namespace = old_attr.namespace().clone();
                let reaction = CallbackReaction::AttributeChanged(
                    old_name,
                    Some(old_value),
                    Some(new_value),
                    namespace,
                );
                ScriptThread::enqueue_callback_reaction(self, reaction, None);
            }
            self.will_mutate_attr(attr);
            attr.set_owner(Some(self));
            self.attrs.borrow_mut()[position] = Dom::from_ref(attr);
            old_attr.set_owner(None);
            if attr.namespace() == &ns!() {
                vtable.attribute_mutated(&attr, AttributeMutation::Set(Some(&old_attr.value())));
            }

            // Step 6.
            Ok(Some(old_attr))
        } else {
            // Step 5.
            attr.set_owner(Some(self));
            self.push_attribute(attr);

            // Step 6.
            Ok(None)
        }
    }

    // https://dom.spec.whatwg.org/#dom-element-setattributenodens
    fn SetAttributeNodeNS(&self, attr: &Attr) -> Fallible<Option<DomRoot<Attr>>> {
        self.SetAttributeNode(attr)
    }

    // https://dom.spec.whatwg.org/#dom-element-removeattribute
    fn RemoveAttribute(&self, name: DOMString) {
        let name = self.parsed_name(name);
        self.remove_attribute_by_name(&name);
    }

    // https://dom.spec.whatwg.org/#dom-element-removeattributens
    fn RemoveAttributeNS(&self, namespace: Option<DOMString>, local_name: DOMString) {
        let namespace = namespace_from_domstring(namespace);
        let local_name = LocalName::from(local_name);
        self.remove_attribute(&namespace, &local_name);
    }

    // https://dom.spec.whatwg.org/#dom-element-removeattributenode
    fn RemoveAttributeNode(&self, attr: &Attr) -> Fallible<DomRoot<Attr>> {
        self.remove_first_matching_attribute(|a| a == attr)
            .ok_or(Error::NotFound)
    }

    // https://dom.spec.whatwg.org/#dom-element-hasattribute
    fn HasAttribute(&self, name: DOMString) -> bool {
        self.GetAttribute(name).is_some()
    }

    // https://dom.spec.whatwg.org/#dom-element-hasattributens
    fn HasAttributeNS(&self, namespace: Option<DOMString>, local_name: DOMString) -> bool {
        self.GetAttributeNS(namespace, local_name).is_some()
    }

    // https://dom.spec.whatwg.org/#dom-element-getelementsbytagname
    fn GetElementsByTagName(&self, localname: DOMString) -> DomRoot<HTMLCollection> {
        let window = window_from_node(self);
        HTMLCollection::by_qualified_name(&window, self.upcast(), LocalName::from(&*localname))
    }

    // https://dom.spec.whatwg.org/#dom-element-getelementsbytagnamens
    fn GetElementsByTagNameNS(
        &self,
        maybe_ns: Option<DOMString>,
        localname: DOMString,
    ) -> DomRoot<HTMLCollection> {
        let window = window_from_node(self);
        HTMLCollection::by_tag_name_ns(&window, self.upcast(), localname, maybe_ns)
    }

    // https://dom.spec.whatwg.org/#dom-element-getelementsbyclassname
    fn GetElementsByClassName(&self, classes: DOMString) -> DomRoot<HTMLCollection> {
        let window = window_from_node(self);
        HTMLCollection::by_class_name(&window, self.upcast(), classes)
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-getclientrects
    fn GetClientRects(&self) -> Vec<DomRoot<DOMRect>> {
        let win = window_from_node(self);
        let raw_rects = self.upcast::<Node>().content_boxes();
        raw_rects
            .iter()
            .map(|rect| {
                DOMRect::new(
                    win.upcast(),
                    rect.origin.x.to_f64_px(),
                    rect.origin.y.to_f64_px(),
                    rect.size.width.to_f64_px(),
                    rect.size.height.to_f64_px(),
                )
            }).collect()
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-getboundingclientrect
    fn GetBoundingClientRect(&self) -> DomRoot<DOMRect> {
        let win = window_from_node(self);
        let rect = self.upcast::<Node>().bounding_content_box_or_zero();
        DOMRect::new(
            win.upcast(),
            rect.origin.x.to_f64_px(),
            rect.origin.y.to_f64_px(),
            rect.size.width.to_f64_px(),
            rect.size.height.to_f64_px(),
        )
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scroll
    fn Scroll(&self, options: &ScrollToOptions) {
        // Step 1
        let left = options.left.unwrap_or(self.ScrollLeft());
        let top = options.top.unwrap_or(self.ScrollTop());
        self.scroll(left, top, options.parent.behavior);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scroll
    fn Scroll_(&self, x: f64, y: f64) {
        self.scroll(x, y, ScrollBehavior::Auto);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrollto
    fn ScrollTo(&self, options: &ScrollToOptions) {
        self.Scroll(options);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrollto
    fn ScrollTo_(&self, x: f64, y: f64) {
        self.Scroll_(x, y);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrollby
    fn ScrollBy(&self, options: &ScrollToOptions) {
        // Step 2
        let delta_left = options.left.unwrap_or(0.0f64);
        let delta_top = options.top.unwrap_or(0.0f64);
        let left = self.ScrollLeft();
        let top = self.ScrollTop();
        self.scroll(left + delta_left, top + delta_top, options.parent.behavior);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrollby
    fn ScrollBy_(&self, x: f64, y: f64) {
        let left = self.ScrollLeft();
        let top = self.ScrollTop();
        self.scroll(left + x, top + y, ScrollBehavior::Auto);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrolltop
    fn ScrollTop(&self) -> f64 {
        let node = self.upcast::<Node>();

        // Step 1
        let doc = node.owner_doc();

        // Step 2
        if !doc.is_fully_active() {
            return 0.0;
        }

        // Step 3
        let win = match doc.GetDefaultView() {
            None => return 0.0,
            Some(win) => win,
        };

        // Step 5
        if *self.root_element() == *self {
            if doc.quirks_mode() == QuirksMode::Quirks {
                return 0.0;
            }

            // Step 6
            return win.ScrollY() as f64;
        }

        // Step 7
        if doc.GetBody().r() == self.downcast::<HTMLElement>() &&
            doc.quirks_mode() == QuirksMode::Quirks &&
            !self.potentially_scrollable()
        {
            return win.ScrollY() as f64;
        }

        // Step 8
        if !self.has_css_layout_box() {
            return 0.0;
        }

        // Step 9
        let point = node.scroll_offset();
        return point.y.abs() as f64;
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrolltop
    fn SetScrollTop(&self, y_: f64) {
        let behavior = ScrollBehavior::Auto;

        // Step 1, 2
        let y = if y_.is_finite() { y_ } else { 0.0f64 };

        let node = self.upcast::<Node>();

        // Step 3
        let doc = node.owner_doc();

        // Step 4
        if !doc.is_fully_active() {
            return;
        }

        // Step 5
        let win = match doc.GetDefaultView() {
            None => return,
            Some(win) => win,
        };

        // Step 7
        if *self.root_element() == *self {
            if doc.quirks_mode() != QuirksMode::Quirks {
                win.scroll(win.ScrollX() as f64, y, behavior);
            }

            return;
        }

        // Step 9
        if doc.GetBody().r() == self.downcast::<HTMLElement>() &&
            doc.quirks_mode() == QuirksMode::Quirks &&
            !self.potentially_scrollable()
        {
            win.scroll(win.ScrollX() as f64, y, behavior);
            return;
        }

        // Step 10
        if !self.has_css_layout_box() || !self.has_scrolling_box() || !self.has_overflow() {
            return;
        }

        // Step 11
        win.scroll_node(node, self.ScrollLeft(), y, behavior);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrolltop
    fn ScrollLeft(&self) -> f64 {
        let node = self.upcast::<Node>();

        // Step 1
        let doc = node.owner_doc();

        // Step 2
        if !doc.is_fully_active() {
            return 0.0;
        }

        // Step 3
        let win = match doc.GetDefaultView() {
            None => return 0.0,
            Some(win) => win,
        };

        // Step 5
        if *self.root_element() == *self {
            if doc.quirks_mode() != QuirksMode::Quirks {
                // Step 6
                return win.ScrollX() as f64;
            }

            return 0.0;
        }

        // Step 7
        if doc.GetBody().r() == self.downcast::<HTMLElement>() &&
            doc.quirks_mode() == QuirksMode::Quirks &&
            !self.potentially_scrollable()
        {
            return win.ScrollX() as f64;
        }

        // Step 8
        if !self.has_css_layout_box() {
            return 0.0;
        }

        // Step 9
        let point = node.scroll_offset();
        return point.x.abs() as f64;
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrollleft
    fn SetScrollLeft(&self, x_: f64) {
        let behavior = ScrollBehavior::Auto;

        // Step 1, 2
        let x = if x_.is_finite() { x_ } else { 0.0f64 };

        let node = self.upcast::<Node>();

        // Step 3
        let doc = node.owner_doc();

        // Step 4
        if !doc.is_fully_active() {
            return;
        }

        // Step 5
        let win = match doc.GetDefaultView() {
            None => return,
            Some(win) => win,
        };

        // Step 7
        if *self.root_element() == *self {
            if doc.quirks_mode() == QuirksMode::Quirks {
                return;
            }

            win.scroll(x, win.ScrollY() as f64, behavior);
            return;
        }

        // Step 9
        if doc.GetBody().r() == self.downcast::<HTMLElement>() &&
            doc.quirks_mode() == QuirksMode::Quirks &&
            !self.potentially_scrollable()
        {
            win.scroll(x, win.ScrollY() as f64, behavior);
            return;
        }

        // Step 10
        if !self.has_css_layout_box() || !self.has_scrolling_box() || !self.has_overflow() {
            return;
        }

        // Step 11
        win.scroll_node(node, x, self.ScrollTop(), behavior);
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrollwidth
    fn ScrollWidth(&self) -> i32 {
        self.upcast::<Node>().scroll_area().size.width
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-scrollheight
    fn ScrollHeight(&self) -> i32 {
        self.upcast::<Node>().scroll_area().size.height
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-clienttop
    fn ClientTop(&self) -> i32 {
        self.upcast::<Node>().client_rect().origin.y
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-clientleft
    fn ClientLeft(&self) -> i32 {
        self.upcast::<Node>().client_rect().origin.x
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-clientwidth
    fn ClientWidth(&self) -> i32 {
        self.upcast::<Node>().client_rect().size.width
    }

    // https://drafts.csswg.org/cssom-view/#dom-element-clientheight
    fn ClientHeight(&self) -> i32 {
        self.upcast::<Node>().client_rect().size.height
    }

    /// <https://w3c.github.io/DOM-Parsing/#widl-Element-innerHTML>
    fn GetInnerHTML(&self) -> Fallible<DOMString> {
        let qname = QualName::new(
            self.prefix().clone(),
            self.namespace().clone(),
            self.local_name().clone(),
        );
        if document_from_node(self).is_html_document() {
            return self.serialize(ChildrenOnly(Some(qname)));
        } else {
            return self.xmlSerialize(XmlChildrenOnly(Some(qname)));
        }
    }

    /// <https://w3c.github.io/DOM-Parsing/#widl-Element-innerHTML>
    fn SetInnerHTML(&self, value: DOMString) -> ErrorResult {
        // Step 1.
        let frag = self.parse_fragment(value)?;
        // Step 2.
        // https://github.com/w3c/DOM-Parsing/issues/1
        let target = if let Some(template) = self.downcast::<HTMLTemplateElement>() {
            DomRoot::upcast(template.Content())
        } else {
            DomRoot::from_ref(self.upcast())
        };
        Node::replace_all(Some(frag.upcast()), &target);
        Ok(())
    }

    // https://dvcs.w3.org/hg/innerhtml/raw-file/tip/index.html#widl-Element-outerHTML
    fn GetOuterHTML(&self) -> Fallible<DOMString> {
        if document_from_node(self).is_html_document() {
            return self.serialize(IncludeNode);
        } else {
            return self.xmlSerialize(XmlIncludeNode);
        }
    }

    // https://w3c.github.io/DOM-Parsing/#dom-element-outerhtml
    fn SetOuterHTML(&self, value: DOMString) -> ErrorResult {
        let context_document = document_from_node(self);
        let context_node = self.upcast::<Node>();
        // Step 1.
        let context_parent = match context_node.GetParentNode() {
            None => {
                // Step 2.
                return Ok(());
            },
            Some(parent) => parent,
        };

        let parent = match context_parent.type_id() {
            // Step 3.
            NodeTypeId::Document(_) => return Err(Error::NoModificationAllowed),

            // Step 4.
            NodeTypeId::DocumentFragment => {
                let body_elem = Element::create(
                    QualName::new(None, ns!(html), local_name!("body")),
                    None,
                    &context_document,
                    ElementCreator::ScriptCreated,
                    CustomElementCreationMode::Synchronous,
                );
                DomRoot::upcast(body_elem)
            },
            _ => context_node.GetParentElement().unwrap(),
        };

        // Step 5.
        let frag = parent.parse_fragment(value)?;
        // Step 6.
        context_parent.ReplaceChild(frag.upcast(), context_node)?;
        Ok(())
    }

    // https://dom.spec.whatwg.org/#dom-nondocumenttypechildnode-previouselementsibling
    fn GetPreviousElementSibling(&self) -> Option<DomRoot<Element>> {
        self.upcast::<Node>()
            .preceding_siblings()
            .filter_map(DomRoot::downcast)
            .next()
    }

    // https://dom.spec.whatwg.org/#dom-nondocumenttypechildnode-nextelementsibling
    fn GetNextElementSibling(&self) -> Option<DomRoot<Element>> {
        self.upcast::<Node>()
            .following_siblings()
            .filter_map(DomRoot::downcast)
            .next()
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-children
    fn Children(&self) -> DomRoot<HTMLCollection> {
        let window = window_from_node(self);
        HTMLCollection::children(&window, self.upcast())
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-firstelementchild
    fn GetFirstElementChild(&self) -> Option<DomRoot<Element>> {
        self.upcast::<Node>().child_elements().next()
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-lastelementchild
    fn GetLastElementChild(&self) -> Option<DomRoot<Element>> {
        self.upcast::<Node>()
            .rev_children()
            .filter_map(DomRoot::downcast::<Element>)
            .next()
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-childelementcount
    fn ChildElementCount(&self) -> u32 {
        self.upcast::<Node>().child_elements().count() as u32
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-prepend
    fn Prepend(&self, nodes: Vec<NodeOrString>) -> ErrorResult {
        self.upcast::<Node>().prepend(nodes)
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-append
    fn Append(&self, nodes: Vec<NodeOrString>) -> ErrorResult {
        self.upcast::<Node>().append(nodes)
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-queryselector
    fn QuerySelector(&self, selectors: DOMString) -> Fallible<Option<DomRoot<Element>>> {
        let root = self.upcast::<Node>();
        root.query_selector(selectors)
    }

    // https://dom.spec.whatwg.org/#dom-parentnode-queryselectorall
    fn QuerySelectorAll(&self, selectors: DOMString) -> Fallible<DomRoot<NodeList>> {
        let root = self.upcast::<Node>();
        root.query_selector_all(selectors)
    }

    // https://dom.spec.whatwg.org/#dom-childnode-before
    fn Before(&self, nodes: Vec<NodeOrString>) -> ErrorResult {
        self.upcast::<Node>().before(nodes)
    }

    // https://dom.spec.whatwg.org/#dom-childnode-after
    fn After(&self, nodes: Vec<NodeOrString>) -> ErrorResult {
        self.upcast::<Node>().after(nodes)
    }

    // https://dom.spec.whatwg.org/#dom-childnode-replacewith
    fn ReplaceWith(&self, nodes: Vec<NodeOrString>) -> ErrorResult {
        self.upcast::<Node>().replace_with(nodes)
    }

    // https://dom.spec.whatwg.org/#dom-childnode-remove
    fn Remove(&self) {
        self.upcast::<Node>().remove_self();
    }

    // https://dom.spec.whatwg.org/#dom-element-matches
    fn Matches(&self, selectors: DOMString) -> Fallible<bool> {
        let selectors = match SelectorParser::parse_author_origin_no_namespace(&selectors) {
            Err(_) => return Err(Error::Syntax),
            Ok(selectors) => selectors,
        };

        let quirks_mode = document_from_node(self).quirks_mode();
        let element = DomRoot::from_ref(self);

        Ok(dom_apis::element_matches(&element, &selectors, quirks_mode))
    }

    // https://dom.spec.whatwg.org/#dom-element-webkitmatchesselector
    fn WebkitMatchesSelector(&self, selectors: DOMString) -> Fallible<bool> {
        self.Matches(selectors)
    }

    // https://dom.spec.whatwg.org/#dom-element-closest
    fn Closest(&self, selectors: DOMString) -> Fallible<Option<DomRoot<Element>>> {
        let selectors = match SelectorParser::parse_author_origin_no_namespace(&selectors) {
            Err(_) => return Err(Error::Syntax),
            Ok(selectors) => selectors,
        };

        let quirks_mode = document_from_node(self).quirks_mode();
        Ok(dom_apis::element_closest(
            DomRoot::from_ref(self),
            &selectors,
            quirks_mode,
        ))
    }

    // https://dom.spec.whatwg.org/#dom-element-insertadjacentelement
    fn InsertAdjacentElement(
        &self,
        where_: DOMString,
        element: &Element,
    ) -> Fallible<Option<DomRoot<Element>>> {
        let where_ = where_.parse::<AdjacentPosition>()?;
        let inserted_node = self.insert_adjacent(where_, element.upcast())?;
        Ok(inserted_node.map(|node| DomRoot::downcast(node).unwrap()))
    }

    // https://dom.spec.whatwg.org/#dom-element-insertadjacenttext
    fn InsertAdjacentText(&self, where_: DOMString, data: DOMString) -> ErrorResult {
        // Step 1.
        let text = Text::new(data, &document_from_node(self));

        // Step 2.
        let where_ = where_.parse::<AdjacentPosition>()?;
        self.insert_adjacent(where_, text.upcast()).map(|_| ())
    }

    // https://w3c.github.io/DOM-Parsing/#dom-element-insertadjacenthtml
    fn InsertAdjacentHTML(&self, position: DOMString, text: DOMString) -> ErrorResult {
        // Step 1.
        let position = position.parse::<AdjacentPosition>()?;

        let context = match position {
            AdjacentPosition::BeforeBegin | AdjacentPosition::AfterEnd => match self
                .upcast::<Node>()
                .GetParentNode()
            {
                Some(ref node) if node.is::<Document>() => return Err(Error::NoModificationAllowed),
                None => return Err(Error::NoModificationAllowed),
                Some(node) => node,
            },
            AdjacentPosition::AfterBegin | AdjacentPosition::BeforeEnd => {
                DomRoot::from_ref(self.upcast::<Node>())
            },
        };

        // Step 2.
        let context =
            Element::fragment_parsing_context(&context.owner_doc(), context.downcast::<Element>());

        // Step 3.
        let fragment = context.parse_fragment(text)?;

        // Step 4.
        self.insert_adjacent(position, fragment.upcast())
            .map(|_| ())
    }

    // check-tidy: no specs after this line
    fn EnterFormalActivationState(&self) -> ErrorResult {
        match self.as_maybe_activatable() {
            Some(a) => {
                a.enter_formal_activation_state();
                return Ok(());
            },
            None => return Err(Error::NotSupported),
        }
    }

    fn ExitFormalActivationState(&self) -> ErrorResult {
        match self.as_maybe_activatable() {
            Some(a) => {
                a.exit_formal_activation_state();
                return Ok(());
            },
            None => return Err(Error::NotSupported),
        }
    }

    // https://fullscreen.spec.whatwg.org/#dom-element-requestfullscreen
    #[allow(unrooted_must_root)]
    fn RequestFullscreen(&self) -> Rc<Promise> {
        let doc = document_from_node(self);
        doc.enter_fullscreen(self)
    }
}

impl VirtualMethods for Element {
    fn super_type(&self) -> Option<&VirtualMethods> {
        Some(self.upcast::<Node>() as &VirtualMethods)
    }

    fn attribute_affects_presentational_hints(&self, attr: &Attr) -> bool {
        // FIXME: This should be more fine-grained, not all elements care about these.
        if attr.local_name() == &local_name!("width") || attr.local_name() == &local_name!("height")
        {
            return true;
        }

        self.super_type()
            .unwrap()
            .attribute_affects_presentational_hints(attr)
    }

    fn attribute_mutated(&self, attr: &Attr, mutation: AttributeMutation) {
        self.super_type().unwrap().attribute_mutated(attr, mutation);
        let node = self.upcast::<Node>();
        let doc = node.owner_doc();
        match attr.local_name() {
            &local_name!("style") => {
                // Modifying the `style` attribute might change style.
                *self.style_attribute.borrow_mut() = match mutation {
                    AttributeMutation::Set(..) => {
                        // This is the fast path we use from
                        // CSSStyleDeclaration.
                        //
                        // Juggle a bit to keep the borrow checker happy
                        // while avoiding the extra clone.
                        let is_declaration = match *attr.value() {
                            AttrValue::Declaration(..) => true,
                            _ => false,
                        };

                        let block = if is_declaration {
                            let mut value = AttrValue::String(String::new());
                            attr.swap_value(&mut value);
                            let (serialization, block) = match value {
                                AttrValue::Declaration(s, b) => (s, b),
                                _ => unreachable!(),
                            };
                            let mut value = AttrValue::String(serialization);
                            attr.swap_value(&mut value);
                            block
                        } else {
                            let win = window_from_node(self);
                            Arc::new(doc.style_shared_lock().wrap(parse_style_attribute(
                                &attr.value(),
                                &doc.base_url(),
                                win.css_error_reporter(),
                                doc.quirks_mode(),
                            )))
                        };

                        Some(block)
                    },
                    AttributeMutation::Removed => None,
                };
            },
            &local_name!("id") => {
                *self.id_attribute.borrow_mut() = mutation.new_value(attr).and_then(|value| {
                    let value = value.as_atom();
                    if value != &atom!("") {
                        Some(value.clone())
                    } else {
                        None
                    }
                });
                if node.is_in_doc() {
                    let value = attr.value().as_atom().clone();
                    match mutation {
                        AttributeMutation::Set(old_value) => {
                            if let Some(old_value) = old_value {
                                let old_value = old_value.as_atom().clone();
                                doc.unregister_named_element(self, old_value);
                            }
                            if value != atom!("") {
                                doc.register_named_element(self, value);
                            }
                        },
                        AttributeMutation::Removed => {
                            if value != atom!("") {
                                doc.unregister_named_element(self, value);
                            }
                        },
                    }
                }
            },
            _ => {
                // FIXME(emilio): This is pretty dubious, and should be done in
                // the relevant super-classes.
                if attr.namespace() == &ns!() && attr.local_name() == &local_name!("src") {
                    node.dirty(NodeDamage::OtherNodeDamage);
                }
            },
        };

        // Make sure we rev the version even if we didn't dirty the node. If we
        // don't do this, various attribute-dependent htmlcollections (like those
        // generated by getElementsByClassName) might become stale.
        node.rev_version();
    }

    fn parse_plain_attribute(&self, name: &LocalName, value: DOMString) -> AttrValue {
        match name {
            &local_name!("id") => AttrValue::from_atomic(value.into()),
            &local_name!("class") => AttrValue::from_serialized_tokenlist(value.into()),
            _ => self
                .super_type()
                .unwrap()
                .parse_plain_attribute(name, value),
        }
    }

    fn bind_to_tree(&self, tree_in_doc: bool) {
        if let Some(ref s) = self.super_type() {
            s.bind_to_tree(tree_in_doc);
        }

        if let Some(f) = self.as_maybe_form_control() {
            f.bind_form_control_to_tree();
        }

        if !tree_in_doc {
            return;
        }

        let doc = document_from_node(self);
        if let Some(ref value) = *self.id_attribute.borrow() {
            doc.register_named_element(self, value.clone());
        }
        // This is used for layout optimization.
        doc.increment_dom_count();
    }

    fn unbind_from_tree(&self, context: &UnbindContext) {
        self.super_type().unwrap().unbind_from_tree(context);

        if let Some(f) = self.as_maybe_form_control() {
            f.unbind_form_control_from_tree();
        }

        if !context.tree_in_doc {
            return;
        }

        let doc = document_from_node(self);
        let fullscreen = doc.GetFullscreenElement();
        if fullscreen.r() == Some(self) {
            doc.exit_fullscreen();
        }
        if let Some(ref value) = *self.id_attribute.borrow() {
            doc.unregister_named_element(self, value.clone());
        }
        // This is used for layout optimization.
        doc.decrement_dom_count();
    }

    fn children_changed(&self, mutation: &ChildrenMutation) {
        if let Some(ref s) = self.super_type() {
            s.children_changed(mutation);
        }

        let flags = self.selector_flags.get();
        if flags.intersects(ElementSelectorFlags::HAS_SLOW_SELECTOR) {
            // All children of this node need to be restyled when any child changes.
            self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
        } else {
            if flags.intersects(ElementSelectorFlags::HAS_SLOW_SELECTOR_LATER_SIBLINGS) {
                if let Some(next_child) = mutation.next_child() {
                    for child in next_child.inclusively_following_siblings() {
                        if child.is::<Element>() {
                            child.dirty(NodeDamage::OtherNodeDamage);
                        }
                    }
                }
            }
            if flags.intersects(ElementSelectorFlags::HAS_EDGE_CHILD_SELECTOR) {
                if let Some(child) = mutation.modified_edge_element() {
                    child.dirty(NodeDamage::OtherNodeDamage);
                }
            }
        }
    }

    fn adopting_steps(&self, old_doc: &Document) {
        self.super_type().unwrap().adopting_steps(old_doc);

        if document_from_node(self).is_html_document() != old_doc.is_html_document() {
            self.tag_name.clear();
        }
    }
}

impl<'a> SelectorsElement for DomRoot<Element> {
    type Impl = SelectorImpl;

    #[allow(unsafe_code)]
    fn opaque(&self) -> ::selectors::OpaqueElement {
        ::selectors::OpaqueElement::new(unsafe {
            &*self.reflector().get_jsobject().get()
        })
    }

    fn parent_element(&self) -> Option<DomRoot<Element>> {
        self.upcast::<Node>().GetParentElement()
    }

    fn parent_node_is_shadow_root(&self) -> bool {
        false
    }

    fn containing_shadow_host(&self) -> Option<Self> {
        None
    }

    fn match_pseudo_element(
        &self,
        _pseudo: &PseudoElement,
        _context: &mut MatchingContext<Self::Impl>,
    ) -> bool {
        false
    }

    fn prev_sibling_element(&self) -> Option<DomRoot<Element>> {
        self.node
            .preceding_siblings()
            .filter_map(DomRoot::downcast)
            .next()
    }

    fn next_sibling_element(&self) -> Option<DomRoot<Element>> {
        self.node
            .following_siblings()
            .filter_map(DomRoot::downcast)
            .next()
    }

    fn attr_matches(
        &self,
        ns: &NamespaceConstraint<&Namespace>,
        local_name: &LocalName,
        operation: &AttrSelectorOperation<&String>,
    ) -> bool {
        match *ns {
            NamespaceConstraint::Specific(ref ns) => self
                .get_attribute(ns, local_name)
                .map_or(false, |attr| attr.value().eval_selector(operation)),
            NamespaceConstraint::Any => self.attrs.borrow().iter().any(|attr| {
                attr.local_name() == local_name && attr.value().eval_selector(operation)
            }),
        }
    }

    fn is_root(&self) -> bool {
        match self.node.GetParentNode() {
            None => false,
            Some(node) => node.is::<Document>(),
        }
    }

    fn is_empty(&self) -> bool {
        self.node.children().all(|node| {
            !node.is::<Element>() && match node.downcast::<Text>() {
                None => true,
                Some(text) => text.upcast::<CharacterData>().data().is_empty(),
            }
        })
    }

    fn local_name(&self) -> &LocalName {
        Element::local_name(self)
    }

    fn namespace(&self) -> &Namespace {
        Element::namespace(self)
    }

    fn match_non_ts_pseudo_class<F>(
        &self,
        pseudo_class: &NonTSPseudoClass,
        _: &mut MatchingContext<Self::Impl>,
        _: &mut F,
    ) -> bool
    where
        F: FnMut(&Self, ElementSelectorFlags),
    {
        match *pseudo_class {
            // https://github.com/servo/servo/issues/8718
            NonTSPseudoClass::Link | NonTSPseudoClass::AnyLink => self.is_link(),
            NonTSPseudoClass::Visited => false,

            NonTSPseudoClass::ServoNonZeroBorder => match self.downcast::<HTMLTableElement>() {
                None => false,
                Some(this) => match this.get_border() {
                    None | Some(0) => false,
                    Some(_) => true,
                },
            },

            NonTSPseudoClass::ServoCaseSensitiveTypeAttr(ref expected_value) => self
                .get_attribute(&ns!(), &local_name!("type"))
                .map_or(false, |attr| attr.value().eq(expected_value)),

            // FIXME(heycam): This is wrong, since extended_filtering accepts
            // a string containing commas (separating each language tag in
            // a list) but the pseudo-class instead should be parsing and
            // storing separate <ident> or <string>s for each language tag.
            NonTSPseudoClass::Lang(ref lang) => extended_filtering(&*self.get_lang(), &*lang),

            NonTSPseudoClass::ReadOnly => !Element::state(self).contains(pseudo_class.state_flag()),

            NonTSPseudoClass::Active |
            NonTSPseudoClass::Focus |
            NonTSPseudoClass::Fullscreen |
            NonTSPseudoClass::Hover |
            NonTSPseudoClass::Enabled |
            NonTSPseudoClass::Disabled |
            NonTSPseudoClass::Checked |
            NonTSPseudoClass::Indeterminate |
            NonTSPseudoClass::ReadWrite |
            NonTSPseudoClass::PlaceholderShown |
            NonTSPseudoClass::Target => Element::state(self).contains(pseudo_class.state_flag()),
        }
    }

    fn is_link(&self) -> bool {
        // FIXME: This is HTML only.
        let node = self.upcast::<Node>();
        match node.type_id() {
            // https://html.spec.whatwg.org/multipage/#selector-link
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLAnchorElement,
            )) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLAreaElement)) |
            NodeTypeId::Element(ElementTypeId::HTMLElement(HTMLElementTypeId::HTMLLinkElement)) => {
                self.has_attribute(&local_name!("href"))
            },
            _ => false,
        }
    }

    fn has_id(&self, id: &Atom, case_sensitivity: CaseSensitivity) -> bool {
        self.id_attribute
            .borrow()
            .as_ref()
            .map_or(false, |atom| case_sensitivity.eq_atom(id, atom))
    }

    fn has_class(&self, name: &Atom, case_sensitivity: CaseSensitivity) -> bool {
        Element::has_class(&**self, name, case_sensitivity)
    }

    fn is_html_element_in_html_document(&self) -> bool {
        self.html_element_in_html_document()
    }

    fn is_html_slot_element(&self) -> bool {
        self.is_html_element() && self.local_name() == &local_name!("slot")
    }
}

impl Element {
    pub fn as_maybe_activatable(&self) -> Option<&Activatable> {
        let element = match self.upcast::<Node>().type_id() {
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLInputElement,
            )) => {
                let element = self.downcast::<HTMLInputElement>().unwrap();
                Some(element as &Activatable)
            },
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLButtonElement,
            )) => {
                let element = self.downcast::<HTMLButtonElement>().unwrap();
                Some(element as &Activatable)
            },
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLAnchorElement,
            )) => {
                let element = self.downcast::<HTMLAnchorElement>().unwrap();
                Some(element as &Activatable)
            },
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLLabelElement,
            )) => {
                let element = self.downcast::<HTMLLabelElement>().unwrap();
                Some(element as &Activatable)
            },
            _ => None,
        };
        element.and_then(|elem| {
            if elem.is_instance_activatable() {
                Some(elem)
            } else {
                None
            }
        })
    }

    pub fn as_stylesheet_owner(&self) -> Option<&StylesheetOwner> {
        if let Some(s) = self.downcast::<HTMLStyleElement>() {
            return Some(s as &StylesheetOwner);
        }

        if let Some(l) = self.downcast::<HTMLLinkElement>() {
            return Some(l as &StylesheetOwner);
        }

        None
    }

    // https://html.spec.whatwg.org/multipage/#category-submit
    pub fn as_maybe_validatable(&self) -> Option<&Validatable> {
        let element = match self.upcast::<Node>().type_id() {
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLInputElement,
            )) => {
                let element = self.downcast::<HTMLInputElement>().unwrap();
                Some(element as &Validatable)
            },
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLButtonElement,
            )) => {
                let element = self.downcast::<HTMLButtonElement>().unwrap();
                Some(element as &Validatable)
            },
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLObjectElement,
            )) => {
                let element = self.downcast::<HTMLObjectElement>().unwrap();
                Some(element as &Validatable)
            },
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLSelectElement,
            )) => {
                let element = self.downcast::<HTMLSelectElement>().unwrap();
                Some(element as &Validatable)
            },
            NodeTypeId::Element(ElementTypeId::HTMLElement(
                HTMLElementTypeId::HTMLTextAreaElement,
            )) => {
                let element = self.downcast::<HTMLTextAreaElement>().unwrap();
                Some(element as &Validatable)
            },
            _ => None,
        };
        element
    }

    pub fn click_in_progress(&self) -> bool {
        self.upcast::<Node>().get_flag(NodeFlags::CLICK_IN_PROGRESS)
    }

    pub fn set_click_in_progress(&self, click: bool) {
        self.upcast::<Node>()
            .set_flag(NodeFlags::CLICK_IN_PROGRESS, click)
    }

    // https://html.spec.whatwg.org/multipage/#nearest-activatable-element
    pub fn nearest_activable_element(&self) -> Option<DomRoot<Element>> {
        match self.as_maybe_activatable() {
            Some(el) => Some(DomRoot::from_ref(el.as_element())),
            None => {
                let node = self.upcast::<Node>();
                for node in node.ancestors() {
                    if let Some(node) = node.downcast::<Element>() {
                        if node.as_maybe_activatable().is_some() {
                            return Some(DomRoot::from_ref(node));
                        }
                    }
                }
                None
            },
        }
    }

    /// Please call this method *only* for real click events
    ///
    /// <https://html.spec.whatwg.org/multipage/#run-authentic-click-activation-steps>
    ///
    /// Use an element's synthetic click activation (or handle_event) for any script-triggered clicks.
    /// If the spec says otherwise, check with Manishearth first
    pub fn authentic_click_activation(&self, event: &Event) {
        // Not explicitly part of the spec, however this helps enforce the invariants
        // required to save state between pre-activation and post-activation
        // since we cannot nest authentic clicks (unlike synthetic click activation, where
        // the script can generate more click events from the handler)
        assert!(!self.click_in_progress());

        let target = self.upcast();
        // Step 2 (requires canvas support)
        // Step 3
        self.set_click_in_progress(true);
        // Step 4
        let e = self.nearest_activable_element();
        match e {
            Some(ref el) => match el.as_maybe_activatable() {
                Some(elem) => {
                    // Step 5-6
                    elem.pre_click_activation();
                    event.fire(target);
                    if !event.DefaultPrevented() {
                        // post click activation
                        elem.activation_behavior(event, target);
                    } else {
                        elem.canceled_activation();
                    }
                },
                // Step 6
                None => {
                    event.fire(target);
                },
            },
            // Step 6
            None => {
                event.fire(target);
            },
        }
        // Step 7
        self.set_click_in_progress(false);
    }

    // https://html.spec.whatwg.org/multipage/#language
    pub fn get_lang(&self) -> String {
        self.upcast::<Node>()
            .inclusive_ancestors()
            .filter_map(|node| {
                node.downcast::<Element>().and_then(|el| {
                    el.get_attribute(&ns!(xml), &local_name!("lang"))
                        .or_else(|| el.get_attribute(&ns!(), &local_name!("lang")))
                        .map(|attr| String::from(attr.Value()))
                })
                // TODO: Check meta tags for a pragma-set default language
                // TODO: Check HTTP Content-Language header
            }).next()
            .unwrap_or(String::new())
    }

    pub fn state(&self) -> ElementState {
        self.state.get()
    }

    pub fn set_state(&self, which: ElementState, value: bool) {
        let mut state = self.state.get();
        if state.contains(which) == value {
            return;
        }
        let node = self.upcast::<Node>();
        node.owner_doc().element_state_will_change(self);
        if value {
            state.insert(which);
        } else {
            state.remove(which);
        }
        self.state.set(state);
    }

    pub fn active_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_ACTIVE_STATE)
    }

    /// <https://html.spec.whatwg.org/multipage/#concept-selector-active>
    pub fn set_active_state(&self, value: bool) {
        self.set_state(ElementState::IN_ACTIVE_STATE, value);

        if let Some(parent) = self.upcast::<Node>().GetParentElement() {
            parent.set_active_state(value);
        }
    }

    pub fn focus_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_FOCUS_STATE)
    }

    pub fn set_focus_state(&self, value: bool) {
        self.set_state(ElementState::IN_FOCUS_STATE, value);
        self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
    }

    pub fn hover_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_HOVER_STATE)
    }

    pub fn set_hover_state(&self, value: bool) {
        self.set_state(ElementState::IN_HOVER_STATE, value)
    }

    pub fn enabled_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_ENABLED_STATE)
    }

    pub fn set_enabled_state(&self, value: bool) {
        self.set_state(ElementState::IN_ENABLED_STATE, value)
    }

    pub fn disabled_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_DISABLED_STATE)
    }

    pub fn set_disabled_state(&self, value: bool) {
        self.set_state(ElementState::IN_DISABLED_STATE, value)
    }

    pub fn read_write_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_READ_WRITE_STATE)
    }

    pub fn set_read_write_state(&self, value: bool) {
        self.set_state(ElementState::IN_READ_WRITE_STATE, value)
    }

    pub fn placeholder_shown_state(&self) -> bool {
        self.state
            .get()
            .contains(ElementState::IN_PLACEHOLDER_SHOWN_STATE)
    }

    pub fn set_placeholder_shown_state(&self, value: bool) {
        if self.placeholder_shown_state() != value {
            self.set_state(ElementState::IN_PLACEHOLDER_SHOWN_STATE, value);
            self.upcast::<Node>().dirty(NodeDamage::OtherNodeDamage);
        }
    }

    pub fn target_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_TARGET_STATE)
    }

    pub fn set_target_state(&self, value: bool) {
        self.set_state(ElementState::IN_TARGET_STATE, value)
    }

    pub fn fullscreen_state(&self) -> bool {
        self.state.get().contains(ElementState::IN_FULLSCREEN_STATE)
    }

    pub fn set_fullscreen_state(&self, value: bool) {
        self.set_state(ElementState::IN_FULLSCREEN_STATE, value)
    }

    /// <https://dom.spec.whatwg.org/#connected>
    pub fn is_connected(&self) -> bool {
        let node = self.upcast::<Node>();
        let root = node.GetRootNode();
        root.is::<Document>()
    }
}

impl Element {
    pub fn check_ancestors_disabled_state_for_form_control(&self) {
        let node = self.upcast::<Node>();
        if self.disabled_state() {
            return;
        }
        for ancestor in node.ancestors() {
            if !ancestor.is::<HTMLFieldSetElement>() {
                continue;
            }
            if !ancestor.downcast::<Element>().unwrap().disabled_state() {
                continue;
            }
            if ancestor.is_parent_of(node) {
                self.set_disabled_state(true);
                self.set_enabled_state(false);
                return;
            }
            if let Some(ref legend) = ancestor.children().find(|n| n.is::<HTMLLegendElement>()) {
                // XXXabinader: should we save previous ancestor to avoid this iteration?
                if node.ancestors().any(|ancestor| ancestor == *legend) {
                    continue;
                }
            }
            self.set_disabled_state(true);
            self.set_enabled_state(false);
            return;
        }
    }

    pub fn check_parent_disabled_state_for_option(&self) {
        if self.disabled_state() {
            return;
        }
        let node = self.upcast::<Node>();
        if let Some(ref parent) = node.GetParentNode() {
            if parent.is::<HTMLOptGroupElement>() &&
                parent.downcast::<Element>().unwrap().disabled_state()
            {
                self.set_disabled_state(true);
                self.set_enabled_state(false);
            }
        }
    }

    pub fn check_disabled_attribute(&self) {
        let has_disabled_attrib = self.has_attribute(&local_name!("disabled"));
        self.set_disabled_state(has_disabled_attrib);
        self.set_enabled_state(!has_disabled_attrib);
    }
}

#[derive(Clone, Copy)]
pub enum AttributeMutation<'a> {
    /// The attribute is set, keep track of old value.
    /// <https://dom.spec.whatwg.org/#attribute-is-set>
    Set(Option<&'a AttrValue>),

    /// The attribute is removed.
    /// <https://dom.spec.whatwg.org/#attribute-is-removed>
    Removed,
}

impl<'a> AttributeMutation<'a> {
    pub fn is_removal(&self) -> bool {
        match *self {
            AttributeMutation::Removed => true,
            AttributeMutation::Set(..) => false,
        }
    }

    pub fn new_value<'b>(&self, attr: &'b Attr) -> Option<Ref<'b, AttrValue>> {
        match *self {
            AttributeMutation::Set(_) => Some(attr.value()),
            AttributeMutation::Removed => None,
        }
    }
}

/// A holder for an element's "tag name", which will be lazily
/// resolved and cached. Should be reset when the document
/// owner changes.
#[derive(JSTraceable, MallocSizeOf)]
struct TagName {
    ptr: DomRefCell<Option<LocalName>>,
}

impl TagName {
    fn new() -> TagName {
        TagName {
            ptr: DomRefCell::new(None),
        }
    }

    /// Retrieve a copy of the current inner value. If it is `None`, it is
    /// initialized with the result of `cb` first.
    fn or_init<F>(&self, cb: F) -> LocalName
    where
        F: FnOnce() -> LocalName,
    {
        match &mut *self.ptr.borrow_mut() {
            &mut Some(ref name) => name.clone(),
            ptr => {
                let name = cb();
                *ptr = Some(name.clone());
                name
            },
        }
    }

    /// Clear the cached tag name, so that it will be re-calculated the
    /// next time that `or_init()` is called.
    fn clear(&self) {
        *self.ptr.borrow_mut() = None;
    }
}

pub struct ElementPerformFullscreenEnter {
    element: Trusted<Element>,
    promise: TrustedPromise,
    error: bool,
}

impl ElementPerformFullscreenEnter {
    pub fn new(
        element: Trusted<Element>,
        promise: TrustedPromise,
        error: bool,
    ) -> Box<ElementPerformFullscreenEnter> {
        Box::new(ElementPerformFullscreenEnter {
            element: element,
            promise: promise,
            error: error,
        })
    }
}

impl TaskOnce for ElementPerformFullscreenEnter {
    #[allow(unrooted_must_root)]
    fn run_once(self) {
        let element = self.element.root();
        let promise = self.promise.root();
        let document = document_from_node(element.r());

        // Step 7.1
        if self.error || !element.fullscreen_element_ready_check() {
            document
                .upcast::<EventTarget>()
                .fire_event(atom!("fullscreenerror"));
            promise.reject_error(Error::Type(String::from("fullscreen is not connected")));
            return;
        }

        // TODO Step 7.2-4
        // Step 7.5
        element.set_fullscreen_state(true);
        document.set_fullscreen_element(Some(&element));
        document
            .window()
            .reflow(ReflowGoal::Full, ReflowReason::ElementStateChanged);

        // Step 7.6
        document
            .upcast::<EventTarget>()
            .fire_event(atom!("fullscreenchange"));

        // Step 7.7
        promise.resolve_native(&());
    }
}

pub struct ElementPerformFullscreenExit {
    element: Trusted<Element>,
    promise: TrustedPromise,
}

impl ElementPerformFullscreenExit {
    pub fn new(
        element: Trusted<Element>,
        promise: TrustedPromise,
    ) -> Box<ElementPerformFullscreenExit> {
        Box::new(ElementPerformFullscreenExit {
            element: element,
            promise: promise,
        })
    }
}

impl TaskOnce for ElementPerformFullscreenExit {
    #[allow(unrooted_must_root)]
    fn run_once(self) {
        let element = self.element.root();
        let document = document_from_node(element.r());
        // TODO Step 9.1-5
        // Step 9.6
        element.set_fullscreen_state(false);

        document
            .window()
            .reflow(ReflowGoal::Full, ReflowReason::ElementStateChanged);

        document.set_fullscreen_element(None);

        // Step 9.8
        document
            .upcast::<EventTarget>()
            .fire_event(atom!("fullscreenchange"));

        // Step 9.10
        self.promise.root().resolve_native(&());
    }
}

pub fn reflect_cross_origin_attribute(element: &Element) -> Option<DOMString> {
    let attr = element.get_attribute(&ns!(), &local_name!("crossorigin"));

    if let Some(mut val) = attr.map(|v| v.Value()) {
        val.make_ascii_lowercase();
        if val == "anonymous" || val == "use-credentials" {
            return Some(val);
        }
        return Some(DOMString::from("anonymous"));
    }
    None
}

pub fn set_cross_origin_attribute(element: &Element, value: Option<DOMString>) {
    match value {
        Some(val) => element.set_string_attribute(&local_name!("crossorigin"), val),
        None => {
            element.remove_attribute(&ns!(), &local_name!("crossorigin"));
        },
    }
}

pub fn cors_setting_for_element(element: &Element) -> Option<CorsSettings> {
    reflect_cross_origin_attribute(element).map_or(None, |attr| match &*attr {
        "anonymous" => Some(CorsSettings::Anonymous),
        "use-credentials" => Some(CorsSettings::UseCredentials),
        _ => unreachable!(),
    })
}