Element.ts

import { is_void } from '../../../shared/utils/names';
import Node from './shared/Node';
import Attribute from './Attribute';
import Binding from './Binding';
import EventHandler from './EventHandler';
import Transition from './Transition';
import Animation from './Animation';
import Action from './Action';
import Class from './Class';
import StyleDirective from './StyleDirective';
import Text from './Text';
import { namespaces } from '../../utils/namespaces';
import map_children from './shared/map_children';
import { dimensions, start_newline } from '../../utils/patterns';
import fuzzymatch from '../../utils/fuzzymatch';
import list from '../../utils/list';
import Let from './Let';
import TemplateScope from './shared/TemplateScope';
import { INode } from './interfaces';
import Component from '../Component';
import Expression from './shared/Expression';
import { string_literal } from '../utils/stringify';
import { Literal } from 'estree';
import compiler_warnings from '../compiler_warnings';
import compiler_errors from '../compiler_errors';
import { ARIARoleDefintionKey, roles, aria, ARIAPropertyDefinition, ARIAProperty } from 'aria-query';

const svg = /^(?:altGlyph|altGlyphDef|altGlyphItem|animate|animateColor|animateMotion|animateTransform|circle|clipPath|color-profile|cursor|defs|desc|discard|ellipse|feBlend|feColorMatrix|feComponentTransfer|feComposite|feConvolveMatrix|feDiffuseLighting|feDisplacementMap|feDistantLight|feDropShadow|feFlood|feFuncA|feFuncB|feFuncG|feFuncR|feGaussianBlur|feImage|feMerge|feMergeNode|feMorphology|feOffset|fePointLight|feSpecularLighting|feSpotLight|feTile|feTurbulence|filter|font|font-face|font-face-format|font-face-name|font-face-src|font-face-uri|foreignObject|g|glyph|glyphRef|hatch|hatchpath|hkern|image|line|linearGradient|marker|mask|mesh|meshgradient|meshpatch|meshrow|metadata|missing-glyph|mpath|path|pattern|polygon|polyline|radialGradient|rect|set|solidcolor|stop|svg|switch|symbol|text|textPath|tref|tspan|unknown|use|view|vkern)$/;

const aria_attributes = 'activedescendant atomic autocomplete busy checked colcount colindex colspan controls current describedby description details disabled dropeffect errormessage expanded flowto grabbed haspopup hidden invalid keyshortcuts label labelledby level live modal multiline multiselectable orientation owns placeholder posinset pressed readonly relevant required roledescription rowcount rowindex rowspan selected setsize sort valuemax valuemin valuenow valuetext'.split(' ');
const aria_attribute_set = new Set(aria_attributes);

const aria_roles = 'alert alertdialog application article banner blockquote button caption cell checkbox code columnheader combobox complementary contentinfo definition deletion dialog directory document emphasis feed figure form generic graphics-document graphics-object graphics-symbol grid gridcell group heading img link list listbox listitem log main marquee math meter menu menubar menuitem menuitemcheckbox menuitemradio navigation none note option paragraph presentation progressbar radio radiogroup region row rowgroup rowheader scrollbar search searchbox separator slider spinbutton status strong subscript superscript switch tab table tablist tabpanel term textbox time timer toolbar tooltip tree treegrid treeitem'.split(' ');
const aria_role_set = new Set(aria_roles);

const a11y_required_attributes = {
	a: ['href'],
	area: ['alt', 'aria-label', 'aria-labelledby'],

	// html-has-lang
	html: ['lang'],

	// iframe-has-title
	iframe: ['title'],
	img: ['alt'],
	object: ['title', 'aria-label', 'aria-labelledby']
};

const a11y_distracting_elements = new Set([
	'blink',
	'marquee'
]);

const a11y_required_content = new Set([
	// anchor-has-content
	'a',

	// heading-has-content
	'h1',
	'h2',
	'h3',
	'h4',
	'h5',
	'h6'
]);

const a11y_labelable = new Set([
	'button',
	'input',
	'keygen',
	'meter',
	'output',
	'progress',
	'select',
	'textarea'
]);

const a11y_nested_implicit_semantics = new Map([
	['header', 'banner'],
	['footer', 'contentinfo']
]);

const a11y_implicit_semantics = new Map([
	['a', 'link'],
	['aside', 'complementary'],
	['body', 'document'],
	['datalist', 'listbox'],
	['dd', 'definition'],
	['dfn', 'term'],
	['details', 'group'],
	['dt', 'term'],
	['fieldset', 'group'],
	['form', 'form'],
	['h1', 'heading'],
	['h2', 'heading'],
	['h3', 'heading'],
	['h4', 'heading'],
	['h5', 'heading'],
	['h6', 'heading'],
	['hr', 'separator'],
	['li', 'listitem'],
	['menu', 'list'],
	['nav', 'navigation'],
	['ol', 'list'],
	['optgroup', 'group'],
	['output', 'status'],
	['progress', 'progressbar'],
	['section', 'region'],
	['summary', 'button'],
	['tbody', 'rowgroup'],
	['textarea', 'textbox'],
	['tfoot', 'rowgroup'],
	['thead', 'rowgroup'],
	['tr', 'row'],
	['ul', 'list']
]);

const invisible_elements = new Set(['meta', 'html', 'script', 'style']);

const valid_modifiers = new Set([
	'preventDefault',
	'stopPropagation',
	'capture',
	'once',
	'passive',
	'nonpassive',
	'self',
	'trusted'
]);

const passive_events = new Set([
	'wheel',
	'touchstart',
	'touchmove',
	'touchend',
	'touchcancel'
]);

const react_attributes = new Map([
	['className', 'class'],
	['htmlFor', 'for']
]);

const attributes_to_compact_whitespace = ['class', 'style'];

function is_parent(parent: INode, elements: string[]) {
	let check = false;

	while (parent) {
		const parent_name = (parent as Element).name;
		if (elements.includes(parent_name)) {
			check = true;
			break;
		}
		if (parent.type === 'Element') {
			break;
		}
		parent = parent.parent;
	}
	return check;
}

function get_namespace(parent: Element, element: Element, explicit_namespace: string) {
	const parent_element = parent.find_nearest(/^Element/);

	if (!parent_element) {
		return explicit_namespace || (svg.test(element.name)
			? namespaces.svg
			: null);
	}

	if (parent_element.namespace !== namespaces.foreign) {
		if (svg.test(element.name.toLowerCase())) return namespaces.svg;
		if (parent_element.name.toLowerCase() === 'foreignobject') return null;
	}

	return parent_element.namespace;
}

function is_valid_aria_attribute_value(schema: ARIAPropertyDefinition, value: string | boolean): boolean {
	switch (schema.type) {
		case 'boolean':
			return typeof value === 'boolean';
		case 'string':
		case 'id':
			return typeof value === 'string';
		case 'tristate':
			return typeof value === 'boolean' || value === 'mixed';
		case 'integer':
		case 'number':
			return typeof value !== 'boolean' && isNaN(Number(value)) === false;
		case 'token': // single token
			return (schema.values || [])
				.indexOf(typeof value === 'string' ? value.toLowerCase() : value) > -1;
		case 'idlist': // if list of ids, split each
			return typeof value === 'string'
				&& value.split(' ').every((id) => typeof id === 'string');
		case 'tokenlist': // if list of tokens, split each
			return typeof value === 'string'
				&& value.split(' ').every((token) => (schema.values || []).indexOf(token.toLowerCase()) > -1);
		default:
			return false;
	}
}

export default class Element extends Node {
	type: 'Element';
	name: string;
	scope: TemplateScope;
	attributes: Attribute[] = [];
	actions: Action[] = [];
	bindings: Binding[] = [];
	classes: Class[] = [];
	styles: StyleDirective[] = [];
	handlers: EventHandler[] = [];
	lets: Let[] = [];
	intro?: Transition = null;
	outro?: Transition = null;
	animation?: Animation = null;
	children: INode[];
	namespace: string;
	needs_manual_style_scoping: boolean;
	tag_expr: Expression;

	get is_dynamic_element() {
		return this.name === 'svelte:element';
	}

	constructor(component: Component, parent: Node, scope: TemplateScope, info: any) {
		super(component, parent, scope, info);
		this.name = info.name;

		if (info.name === 'svelte:element') {
			if (typeof info.tag !== 'string') {
				this.tag_expr = new Expression(component, this, scope, info.tag);
			} else {
				this.tag_expr = new Expression(component, this, scope, string_literal(info.tag) as Literal);
			}
		} else {
			this.tag_expr = new Expression(component, this, scope, string_literal(this.name) as Literal);
		}

		this.namespace = get_namespace(parent as Element, this, component.namespace);

		if (this.namespace !== namespaces.foreign) {
			if (this.name === 'pre' || this.name === 'textarea') {
				const first = info.children[0];
				if (first && first.type === 'Text') {
					// The leading newline character needs to be stripped because of a qirk,
					// it is ignored by browsers if the tag and its contents are set through
					// innerHTML (NOT if set through the innerHTML of the tag or dynamically).
					// Therefore strip it here but add it back in the appropriate
					// places if there's another newline afterwards.
					// see https://html.spec.whatwg.org/multipage/syntax.html#element-restrictions
					// see https://html.spec.whatwg.org/multipage/grouping-content.html#the-pre-element
					first.data = first.data.replace(start_newline, '');
				}
			}

			if (this.name === 'textarea') {
				if (info.children.length > 0) {
					const value_attribute = info.attributes.find(node => node.name === 'value');
					if (value_attribute) {
						component.error(value_attribute, compiler_errors.textarea_duplicate_value);
						return;
					}

					// this is an egregious hack, but it's the easiest way to get <textarea>
					// children treated the same way as a value attribute
					info.attributes.push({
						type: 'Attribute',
						name: 'value',
						value: info.children
					});

					info.children = [];
				}
			}

			if (this.name === 'option') {
				// Special case — treat these the same way:
				//   <option>{foo}</option>
				//   <option value={foo}>{foo}</option>
				const value_attribute = info.attributes.find(attribute => attribute.name === 'value');

				if (!value_attribute) {
					info.attributes.push({
						type: 'Attribute',
						name: 'value',
						value: info.children,
						synthetic: true
					});
				}
			}
		}
		const has_let = info.attributes.some(node => node.type === 'Let');
		if (has_let) {
			scope = scope.child();
		}

		// Binding relies on Attribute, defer its evaluation
		const order = ['Binding']; // everything else is -1
		info.attributes.sort((a, b) => order.indexOf(a.type) - order.indexOf(b.type));

		info.attributes.forEach(node => {
			switch (node.type) {
				case 'Action':
					this.actions.push(new Action(component, this, scope, node));
					break;

				case 'Attribute':
				case 'Spread':
					// special case
					if (node.name === 'xmlns') this.namespace = node.value[0].data;

					this.attributes.push(new Attribute(component, this, scope, node));
					break;

				case 'Binding':
					this.bindings.push(new Binding(component, this, scope, node));
					break;

				case 'Class':
					this.classes.push(new Class(component, this, scope, node));
					break;

				case 'StyleDirective':
					this.styles.push(new StyleDirective(component, this, scope, node));
					break;

				case 'EventHandler':
					this.handlers.push(new EventHandler(component, this, scope, node));
					break;

				case 'Let': {
					const l = new Let(component, this, scope, node);
					this.lets.push(l);
					const dependencies = new Set([l.name.name]);

					l.names.forEach(name => {
						scope.add(name, dependencies, this);
					});
					break;
				}

				case 'Transition':
				{
					const transition = new Transition(component, this, scope, node);
					if (node.intro) this.intro = transition;
					if (node.outro) this.outro = transition;
					break;
				}

				case 'Animation':
					this.animation = new Animation(component, this, scope, node);
					break;

				default:
					throw new Error(`Not implemented: ${node.type}`);
			}
		});

		this.scope = scope;
		this.children = map_children(component, this, this.scope, info.children);

		this.validate();

		this.optimise();

		component.apply_stylesheet(this);
	}

	validate() {
		if (this.component.var_lookup.has(this.name) && this.component.var_lookup.get(this.name).imported) {
			this.component.warn(this, compiler_warnings.component_name_lowercase(this.name));
		}

		this.validate_attributes();
		this.validate_event_handlers();
		if (this.namespace === namespaces.foreign) {
			this.validate_bindings_foreign();
		} else {
			this.validate_attributes_a11y();
			this.validate_special_cases();
			this.validate_bindings();
			this.validate_content();
		}

	}

	validate_attributes() {
		const { component, parent } = this;

		this.attributes.forEach(attribute => {
			if (attribute.is_spread) return;

			const name = attribute.name.toLowerCase();

			// Errors

			if (/(^[0-9-.])|[\^$@%&#?!|()[\]{}^*+~;]/.test(name)) {
				return component.error(attribute, compiler_errors.illegal_attribute(name));
			}

			if (name === 'slot') {
				if (!attribute.is_static) {
					return component.error(attribute, compiler_errors.invalid_slot_attribute);
				}

				if (component.slot_outlets.has(name)) {
					return component.error(attribute, compiler_errors.duplicate_slot_attribute(name));

					// this code was unreachable. Still needed?
					// component.slot_outlets.add(name);
				}

				if (!(parent.type === 'SlotTemplate' || within_custom_element(parent))) {
					return component.error(attribute, compiler_errors.invalid_slotted_content);
				}
			}

			// Warnings

			if (this.namespace !== namespaces.foreign) {
				if (name === 'is') {
					component.warn(attribute, compiler_warnings.avoid_is);
				}

				if (react_attributes.has(attribute.name)) {
					component.warn(attribute, compiler_warnings.invalid_html_attribute(attribute.name, react_attributes.get(attribute.name)));
				}
			}
		});
	}

	validate_attributes_a11y() {
		const { component, attributes } = this;

		attributes.forEach(attribute => {
			if (attribute.is_spread) return;

			const name = attribute.name.toLowerCase();

			// aria-props
			if (name.startsWith('aria-')) {
				if (invisible_elements.has(this.name)) {
					// aria-unsupported-elements
					component.warn(attribute, compiler_warnings.a11y_aria_attributes(this.name));
				}

				const type = name.slice(5);
				if (!aria_attribute_set.has(type)) {
					const match = fuzzymatch(type, aria_attributes);
					component.warn(attribute, compiler_warnings.a11y_unknown_aria_attribute(type, match));
				}

				if (name === 'aria-hidden' && /^h[1-6]$/.test(this.name)) {
					component.warn(attribute, compiler_warnings.a11y_hidden(this.name));
				}

				// aria-proptypes
				let value = attribute.get_static_value();
				if (value === 'true') value = true;
				if (value === 'false') value = false;

				if (value !== null && value !== undefined && aria.has(name as ARIAProperty)) {
					const schema = aria.get(name as ARIAProperty);
					if (!is_valid_aria_attribute_value(schema, value)) {
						component.warn(attribute, compiler_warnings.a11y_incorrect_attribute_type(schema, name));
					}
				}
			}

			// aria-role
			if (name === 'role') {
				if (invisible_elements.has(this.name)) {
					// aria-unsupported-elements
					component.warn(attribute, compiler_warnings.a11y_misplaced_role(this.name));
				}

				const value = attribute.get_static_value();
				// @ts-ignore
				if (value && !aria_role_set.has(value)) {
					// @ts-ignore
					const match = fuzzymatch(value, aria_roles);
					component.warn(attribute, compiler_warnings.a11y_unknown_role(value, match));
				}

				// no-redundant-roles
				const has_redundant_role = value === a11y_implicit_semantics.get(this.name);

				if (this.name === value || has_redundant_role) {
					component.warn(attribute, compiler_warnings.a11y_no_redundant_roles(value));
				}

				// Footers and headers are special cases, and should not have redundant roles unless they are the children of sections or articles.
				const is_parent_section_or_article = is_parent(this.parent, ['section', 'article']);
				if (!is_parent_section_or_article) {
					const has_nested_redundant_role = value === a11y_nested_implicit_semantics.get(this.name);
					if (has_nested_redundant_role) {
						component.warn(attribute, compiler_warnings.a11y_no_redundant_roles(value));
					}
				}

				// role-has-required-aria-props
				const role = roles.get(value as ARIARoleDefintionKey);
				if (role) {
					const required_role_props = Object.keys(role.requiredProps);
					const has_missing_props = required_role_props.some(prop => !attributes.find(a => a.name === prop));

					if (has_missing_props) {
						component.warn(attribute, compiler_warnings.a11y_role_has_required_aria_props(value as string, required_role_props));
					}
				}
			}

			// no-access-key
			if (name === 'accesskey') {
				component.warn(attribute, compiler_warnings.a11y_accesskey);
			}

			// no-autofocus
			if (name === 'autofocus') {
				component.warn(attribute, compiler_warnings.a11y_autofocus);
			}

			// scope
			if (name === 'scope' && this.name !== 'th') {
				component.warn(attribute, compiler_warnings.a11y_misplaced_scope);
			}

			// tabindex-no-positive
			if (name === 'tabindex') {
				const value = attribute.get_static_value();
				// @ts-ignore todo is tabindex=true correct case?
				if (!isNaN(value) && +value > 0) {
					component.warn(attribute, compiler_warnings.a11y_positive_tabindex);
				}
			}
		});
	}


	validate_special_cases() {
		const { component, attributes, handlers } = this;

		const attribute_map = new Map();
		const handlers_map = new Map();

		attributes.forEach(attribute => (
			attribute_map.set(attribute.name, attribute)
		));

		handlers.forEach(handler => (
			handlers_map.set(handler.name, handler)
		));

		if (this.name === 'a') {
			const href_attribute = attribute_map.get('href') || attribute_map.get('xlink:href');
			const id_attribute = attribute_map.get('id');
			const name_attribute = attribute_map.get('name');

			if (href_attribute) {
				const href_value = href_attribute.get_static_value();

				if (href_value === '' || href_value === '#' || /^\W*javascript:/i.test(href_value)) {
					component.warn(href_attribute, compiler_warnings.a11y_invalid_attribute(href_attribute.name, href_value));
				}
			} else {
				const id_attribute_valid = id_attribute && id_attribute.get_static_value() !== '';
				const name_attribute_valid = name_attribute && name_attribute.get_static_value() !== '';

				if (!id_attribute_valid && !name_attribute_valid) {
					component.warn(this, compiler_warnings.a11y_missing_attribute('a', 'an', 'href'));
				}
			}
		} else {
			const required_attributes = a11y_required_attributes[this.name];
			if (required_attributes) {
				const has_attribute = required_attributes.some(name => attribute_map.has(name));

				if (!has_attribute) {
					should_have_attribute(this, required_attributes);
				}
			}
		}

		if (this.name === 'input') {
			const type = attribute_map.get('type');
			if (type && type.get_static_value() === 'image') {
				const required_attributes = ['alt', 'aria-label', 'aria-labelledby'];
				const has_attribute = required_attributes.some(name => attribute_map.has(name));

				if (!has_attribute) {
					should_have_attribute(this, required_attributes, 'input type="image"');
				}
			}
		}

		if (this.name === 'img') {
			const alt_attribute = attribute_map.get('alt');
			const aria_hidden_attribute = attribute_map.get('aria-hidden');

			const aria_hidden_exist = aria_hidden_attribute && aria_hidden_attribute.get_static_value();

			if (alt_attribute && !aria_hidden_exist) {
				const alt_value = alt_attribute.get_static_value();

				if (/\b(image|picture|photo)\b/i.test(alt_value)) {
					component.warn(this, compiler_warnings.a11y_img_redundant_alt);
				}
			}
		}

		if (this.name === 'label') {
			const has_input_child = this.children.some(i => (i instanceof Element && a11y_labelable.has(i.name) ));
			if (!attribute_map.has('for') && !has_input_child) {
				component.warn(this, compiler_warnings.a11y_label_has_associated_control);
			}
		}

		if (this.name === 'video') {
			if (attribute_map.has('muted')) {
				return;
			}

			let has_caption;
			const track = this.children.find((i: Element) => i.name === 'track');
			if (track) {
				has_caption = track.attributes.find(a => a.name === 'kind' && a.get_static_value() === 'captions');
			}

			if (!has_caption) {
				component.warn(this, compiler_warnings.a11y_media_has_caption);
			}
		}

		if (a11y_distracting_elements.has(this.name)) {
			// no-distracting-elements
			component.warn(this, compiler_warnings.a11y_distracting_elements(this.name));
		}

		if (this.name === 'figcaption') {
			let { parent } = this;
			let is_figure_parent = false;

			while (parent) {
				if ((parent as Element).name === 'figure') {
					is_figure_parent = true;
					break;
				}
				if (parent.type === 'Element') {
					break;
				}
				parent = parent.parent;
			}

			if (!is_figure_parent) {
				component.warn(this, compiler_warnings.a11y_structure_immediate);
			}
		}

		if (this.name === 'figure') {
			const children = this.children.filter(node => {
				if (node.type === 'Comment') return false;
				if (node.type === 'Text') return /\S/.test(node.data);
				return true;
			});

			const index = children.findIndex(child => (child as Element).name === 'figcaption');

			if (index !== -1 && (index !== 0 && index !== children.length - 1)) {
				component.warn(children[index], compiler_warnings.a11y_structure_first_or_last);
			}
		}

		if (handlers_map.has('mouseover') && !handlers_map.has('focus')) {
			component.warn(this, compiler_warnings.a11y_mouse_events_have_key_events('mouseover', 'focus'));
		}

		if (handlers_map.has('mouseout') && !handlers_map.has('blur')) {
			component.warn(this, compiler_warnings.a11y_mouse_events_have_key_events('mouseout', 'blur'));
		}
	}

	validate_bindings_foreign() {
		this.bindings.forEach(binding => {
			if (binding.name !== 'this') {
				return this.component.error(binding, compiler_errors.invalid_binding_foreign(binding.name));
			}
		});
	}

	validate_bindings() {
		const { component } = this;

		const check_type_attribute = () => {
			const attribute = this.attributes.find(
				(attribute: Attribute) => attribute.name === 'type'
			);

			if (!attribute) return null;

			if (!attribute.is_static) {
				return component.error(attribute, compiler_errors.invalid_type);
			}

			const value = attribute.get_static_value();

			if (value === true) {
				return component.error(attribute, compiler_errors.missing_type);
			}

			return value;
		};

		this.bindings.forEach(binding => {
			const { name } = binding;

			if (name === 'value') {
				if (
					this.name !== 'input' &&
					this.name !== 'textarea' &&
					this.name !== 'select'
				) {
					return component.error(binding, compiler_errors.invalid_binding_elements(this.name, 'value'));
				}

				if (this.name === 'select') {
					const attribute = this.attributes.find(
						(attribute: Attribute) => attribute.name === 'multiple'
					);

					if (attribute && !attribute.is_static) {
						return component.error(attribute, compiler_errors.dynamic_multiple_attribute);
					}
				} else {
					check_type_attribute();
				}
			} else if (name === 'checked' || name === 'indeterminate') {
				if (this.name !== 'input') {
					return component.error(binding, compiler_errors.invalid_binding_elements(this.name, name));
				}

				const type = check_type_attribute();

				if (type !== 'checkbox') {
					return component.error(binding, compiler_errors.invalid_binding_no_checkbox(name, type === 'radio'));
				}
			} else if (name === 'group') {
				if (this.name !== 'input') {
					return component.error(binding, compiler_errors.invalid_binding_elements(this.name, 'group'));
				}

				const type = check_type_attribute();

				if (type !== 'checkbox' && type !== 'radio') {
					return component.error(binding, compiler_errors.invalid_binding_element_with('<input type="checkbox"> or <input type="radio">', 'group'));
				}
			} else if (name === 'files') {
				if (this.name !== 'input') {
					return component.error(binding, compiler_errors.invalid_binding_elements(this.name, 'files'));
				}

				const type = check_type_attribute();

				if (type !== 'file') {
					return component.error(binding, compiler_errors.invalid_binding_element_with('<input type="file">', 'files'));
				}

			} else if (name === 'open') {
				if (this.name !== 'details') {
					return component.error(binding, compiler_errors.invalid_binding_element_with('<details>', name));
				}
			} else if (
				name === 'currentTime' ||
				name === 'duration' ||
				name === 'paused' ||
				name === 'buffered' ||
				name === 'seekable' ||
				name === 'played' ||
				name === 'volume' ||
				name === 'muted' ||
				name === 'playbackRate' ||
				name === 'seeking' ||
				name === 'ended'
			) {
				if (this.name !== 'audio' && this.name !== 'video') {
					return component.error(binding, compiler_errors.invalid_binding_element_with('audio> or <video>', name));
				}
			} else if (
				name === 'videoHeight' ||
				name === 'videoWidth'
			) {
				if (this.name !== 'video') {
					return component.error(binding, compiler_errors.invalid_binding_element_with('<video>', name));
				}
			} else if (dimensions.test(name)) {
				if (this.name === 'svg' && (name === 'offsetWidth' || name === 'offsetHeight')) {
					return component.error(binding, compiler_errors.invalid_binding_on(binding.name, `<svg>. Use '${name.replace('offset', 'client')}' instead`));
				} else if (svg.test(this.name)) {
					return component.error(binding, compiler_errors.invalid_binding_on(binding.name, 'SVG elements'));
				} else if (is_void(this.name)) {
					return component.error(binding, compiler_errors.invalid_binding_on(binding.name, `void elements like <${this.name}>. Use a wrapper element instead`));
				}
			} else if (
				name === 'textContent' ||
				name === 'innerHTML'
			) {
				const contenteditable = this.attributes.find(
					(attribute: Attribute) => attribute.name === 'contenteditable'
				);

				if (!contenteditable) {
					return component.error(binding, compiler_errors.missing_contenteditable_attribute);
				} else if (contenteditable && !contenteditable.is_static) {
					return component.error(contenteditable, compiler_errors.dynamic_contenteditable_attribute);
				}
			} else if (name !== 'this') {
				return component.error(binding, compiler_errors.invalid_binding(binding.name));
			}
		});
	}

	validate_content() {
		if (!a11y_required_content.has(this.name)) return;
		if (
			this.bindings
				.some((binding) => ['textContent', 'innerHTML'].includes(binding.name))
		) return;

		if (this.children.length === 0) {
			this.component.warn(this, compiler_warnings.a11y_missing_content(this.name));
		}
	}

	validate_event_handlers() {
		const { component } = this;

		this.handlers.forEach(handler => {
			if (handler.modifiers.has('passive') && handler.modifiers.has('preventDefault')) {
				return component.error(handler, compiler_errors.invalid_event_modifier_combination('passive', 'preventDefault'));
			}

			if (handler.modifiers.has('passive') && handler.modifiers.has('nonpassive')) {
				return component.error(handler, compiler_errors.invalid_event_modifier_combination('passive', 'nonpassive'));
			}

			handler.modifiers.forEach(modifier => {
				if (!valid_modifiers.has(modifier)) {
					return component.error(handler, compiler_errors.invalid_event_modifier(list(Array.from(valid_modifiers))));
				}

				if (modifier === 'passive') {
					if (passive_events.has(handler.name)) {
						if (handler.can_make_passive) {
							component.warn(handler, compiler_warnings.redundant_event_modifier_for_touch);
						}
					} else {
						component.warn(handler, compiler_warnings.redundant_event_modifier_passive);
					}
				}

				if (component.compile_options.legacy && (modifier === 'once' || modifier === 'passive')) {
					// TODO this could be supported, but it would need a few changes to
					// how event listeners work
					return component.error(handler, compiler_errors.invalid_event_modifier_legacy(modifier));
				}
			});

			if (passive_events.has(handler.name) && handler.can_make_passive && !handler.modifiers.has('preventDefault') && !handler.modifiers.has('nonpassive')) {
				// touch/wheel events should be passive by default
				handler.modifiers.add('passive');
			}
		});
	}

	is_media_node() {
		return this.name === 'audio' || this.name === 'video';
	}

	add_css_class() {
		if (this.attributes.some(attr => attr.is_spread)) {
			this.needs_manual_style_scoping = true;
			return;
		}

		const { id } = this.component.stylesheet;

		const class_attribute = this.attributes.find(a => a.name === 'class');

		if (class_attribute && !class_attribute.is_true) {
			if (class_attribute.chunks.length === 1 && class_attribute.chunks[0].type === 'Text') {
				(class_attribute.chunks[0] as Text).data += ` ${id}`;
			} else {
				(class_attribute.chunks as Node[]).push(
					new Text(this.component, this, this.scope, {
						type: 'Text',
						data: ` ${id}`,
						synthetic: true
					} as any)
				);
			}
		} else {
			this.attributes.push(
				new Attribute(this.component, this, this.scope, {
					type: 'Attribute',
					name: 'class',
					value: [{ type: 'Text', data: id, synthetic: true }]
				} as any)
			);
		}
	}

	get slot_template_name() {
		return this.attributes.find(attribute => attribute.name === 'slot').get_static_value() as string;
	}

	optimise() {
		attributes_to_compact_whitespace.forEach(attribute_name => {
			const attribute = this.attributes.find(a => a.name === attribute_name);
			if (attribute && !attribute.is_true) {
				attribute.chunks.forEach((chunk, index) => {
					if (chunk.type === 'Text') {
						let data = chunk.data.replace(/[\s\n\t]+/g, ' ');
						if (index === 0) {
							data = data.trimLeft();
						} else if (index === attribute.chunks.length - 1) {
							data = data.trimRight();
						}
						chunk.data = data;
					}
				});
			}
		});
	}
}

function should_have_attribute(
	node,
	attributes: string[],
	name = node.name
) {
	const article = /^[aeiou]/.test(attributes[0]) ? 'an' : 'a';
	const sequence = attributes.length > 1 ?
		attributes.slice(0, -1).join(', ') + ` or ${attributes[attributes.length - 1]}` :
		attributes[0];

	node.component.warn(node, compiler_warnings.a11y_missing_attribute(name, article, sequence));
}

function within_custom_element(parent: INode) {
	while (parent) {
		if (parent.type === 'InlineComponent') return false;
		if (parent.type === 'Element' && /-/.test(parent.name)) return true;
		parent = parent.parent;
	}
	return false;
}