text: /**
   * @license Copyright (c) 2003-2022, CKSource Holding sp. z o.o. All rights reserved.
   * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
   */
  
  /**
   * @module engine/view/domconverter
   */
  
  /* globals document, Node, NodeFilter, DOMParser, Text */
  
  import ViewText from './text';
  import ViewElement from './element';
  import ViewUIElement from './uielement';
  import ViewPosition from './position';
  import ViewRange from './range';
  import ViewSelection from './selection';
  import ViewDocumentFragment from './documentfragment';
  import ViewTreeWalker from './treewalker';
  import Matcher from './matcher';
  import {
  	BR_FILLER, INLINE_FILLER_LENGTH, NBSP_FILLER, MARKED_NBSP_FILLER,
  	getDataWithoutFiller, isInlineFiller, startsWithFiller
  } from './filler';
  
  import global from '@ckeditor/ckeditor5-utils/src/dom/global';
  import { logWarning } from '@ckeditor/ckeditor5-utils/src/ckeditorerror';
  import indexOf from '@ckeditor/ckeditor5-utils/src/dom/indexof';
  import getAncestors from '@ckeditor/ckeditor5-utils/src/dom/getancestors';
  import isText from '@ckeditor/ckeditor5-utils/src/dom/istext';
  import isComment from '@ckeditor/ckeditor5-utils/src/dom/iscomment';
  
  const BR_FILLER_REF = BR_FILLER( document ); // eslint-disable-line new-cap
  const NBSP_FILLER_REF = NBSP_FILLER( document ); // eslint-disable-line new-cap
  const MARKED_NBSP_FILLER_REF = MARKED_NBSP_FILLER( document ); // eslint-disable-line new-cap
  const UNSAFE_ATTRIBUTE_NAME_PREFIX = 'data-ck-unsafe-attribute-';
  const UNSAFE_ELEMENT_REPLACEMENT_ATTRIBUTE = 'data-ck-unsafe-element';
  
  /**
   * `DomConverter` is a set of tools to do transformations between DOM nodes and view nodes. It also handles
   * {@link module:engine/view/domconverter~DomConverter#bindElements bindings} between these nodes.
   *
   * An instance of the DOM converter is available under
   * {@link module:engine/view/view~View#domConverter `editor.editing.view.domConverter`}.
   *
   * The DOM converter does not check which nodes should be rendered (use {@link module:engine/view/renderer~Renderer}), does not keep the
   * state of a tree nor keeps the synchronization between the tree view and the DOM tree (use {@link module:engine/view/document~Document}).
   *
   * The DOM converter keeps DOM elements to view element bindings, so when the converter gets destroyed, the bindings are lost.
   * Two converters will keep separate binding maps, so one tree view can be bound with two DOM trees.
   */
  export default class DomConverter {
  	/**
  	 * Creates a DOM converter.
  	 *
  	 * @param {module:engine/view/document~Document} document The view document instance.
  	 * @param {Object} options An object with configuration options.
  	 * @param {module:engine/view/filler~BlockFillerMode} [options.blockFillerMode] The type of the block filler to use.
  	 * Default value depends on the options.renderingMode:
  	 *  'nbsp' when options.renderingMode == 'data',
  	 *  'br' when options.renderingMode == 'editing'.
  	 * @param {'data'|'editing'} [options.renderingMode='editing'] Whether to leave the View-to-DOM conversion result unchanged
  	 * or improve editing experience by filtering out interactive data.
  	 */
  	constructor( document, options = {} ) {
  		/**
  		 * @readonly
  		 * @type {module:engine/view/document~Document}
  		 */
  		this.document = document;
  
  		/**
  		 * Whether to leave the View-to-DOM conversion result unchanged or improve editing experience by filtering out interactive data.
  		 *
  		 * @member {'data'|'editing'} module:engine/view/domconverter~DomConverter#renderingMode
  		 */
  		this.renderingMode = options.renderingMode || 'editing';
  
  		/**
  		 * The mode of a block filler used by the DOM converter.
  		 *
  		 * @member {'br'|'nbsp'|'markedNbsp'} module:engine/view/domconverter~DomConverter#blockFillerMode
  		 */
  		this.blockFillerMode = options.blockFillerMode || ( this.renderingMode === 'editing' ? 'br' : 'nbsp' );
  
  		/**
  		 * Elements which are considered pre-formatted elements.
  		 *
  		 * @readonly
  		 * @member {Array.<String>} module:engine/view/domconverter~DomConverter#preElements
  		 */
  		this.preElements = [ 'pre' ];
  
  		/**
  		 * Elements which are considered block elements (and hence should be filled with a
  		 * {@link #isBlockFiller block filler}).
  		 *
  		 * Whether an element is considered a block element also affects handling of trailing whitespaces.
  		 *
  		 * You can extend this array if you introduce support for block elements which are not yet recognized here.
  		 *
  		 * @readonly
  		 * @member {Array.<String>} module:engine/view/domconverter~DomConverter#blockElements
  		 */
  		this.blockElements = [
  			'address', 'article', 'aside', 'blockquote', 'caption', 'center', 'dd', 'details', 'dir', 'div',
  			'dl', 'dt', 'fieldset', 'figcaption', 'figure', 'footer', 'form', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'header',
  			'hgroup', 'legend', 'li', 'main', 'menu', 'nav', 'ol', 'p', 'pre', 'section', 'summary', 'table', 'tbody',
  			'td', 'tfoot', 'th', 'thead', 'tr', 'ul'
  		];
  
  		/**
  		 * A list of elements that exist inline (in text) but their inner structure cannot be edited because
  		 * of the way they are rendered by the browser. They are mostly HTML form elements but there are other
  		 * elements such as `<img>` or `<iframe>` that also have non-editable children or no children whatsoever.
  		 *
  		 * Whether an element is considered an inline object has an impact on white space rendering (trimming)
  		 * around (and inside of it). In short, white spaces in text nodes next to inline objects are not trimmed.
  		 *
  		 * You can extend this array if you introduce support for inline object elements which are not yet recognized here.
  		 *
  		 * @readonly
  		 * @member {Array.<String>} module:engine/view/domconverter~DomConverter#inlineObjectElements
  		 */
  		this.inlineObjectElements = [
  			'object', 'iframe', 'input', 'button', 'textarea', 'select', 'option', 'video', 'embed', 'audio', 'img', 'canvas'
  		];
  
  		/**
  		 * The DOM-to-view mapping.
  		 *
  		 * @private
  		 * @member {WeakMap} module:engine/view/domconverter~DomConverter#_domToViewMapping
  		 */
  		this._domToViewMapping = new WeakMap();
  
  		/**
  		 * The view-to-DOM mapping.
  		 *
  		 * @private
  		 * @member {WeakMap} module:engine/view/domconverter~DomConverter#_viewToDomMapping
  		 */
  		this._viewToDomMapping = new WeakMap();
  
  		/**
  		 * Holds the mapping between fake selection containers and corresponding view selections.
  		 *
  		 * @private
  		 * @member {WeakMap} module:engine/view/domconverter~DomConverter#_fakeSelectionMapping
  		 */
  		this._fakeSelectionMapping = new WeakMap();
  
  		/**
  		 * Matcher for view elements whose content should be treated as raw data
  		 * and not processed during the conversion from DOM nodes to view elements.
  		 *
  		 * @private
  		 * @type {module:engine/view/matcher~Matcher}
  		 */
  		this._rawContentElementMatcher = new Matcher();
  
  		/**
  		 * A set of encountered raw content DOM nodes. It is used for preventing left trimming of the following text node.
  		 *
  		 * @private
  		 * @type {WeakSet.<Node>}
  		 */
  		this._encounteredRawContentDomNodes = new WeakSet();
  	}
  
  	/**
  	 * Binds a given DOM element that represents fake selection to a **position** of a
  	 * {@link module:engine/view/documentselection~DocumentSelection document selection}.
  	 * Document selection copy is stored and can be retrieved by the
  	 * {@link module:engine/view/domconverter~DomConverter#fakeSelectionToView} method.
  	 *
  	 * @param {HTMLElement} domElement
  	 * @param {module:engine/view/documentselection~DocumentSelection} viewDocumentSelection
  	 */
  	bindFakeSelection( domElement, viewDocumentSelection ) {
  		this._fakeSelectionMapping.set( domElement, new ViewSelection( viewDocumentSelection ) );
  	}
  
  	/**
  	 * Returns a {@link module:engine/view/selection~Selection view selection} instance corresponding to a given
  	 * DOM element that represents fake selection. Returns `undefined` if binding to the given DOM element does not exist.
  	 *
  	 * @param {HTMLElement} domElement
  	 * @returns {module:engine/view/selection~Selection|undefined}
  	 */
  	fakeSelectionToView( domElement ) {
  		return this._fakeSelectionMapping.get( domElement );
  	}
  
  	/**
  	 * Binds DOM and view elements, so it will be possible to get corresponding elements using
  	 * {@link module:engine/view/domconverter~DomConverter#mapDomToView} and
  	 * {@link module:engine/view/domconverter~DomConverter#mapViewToDom}.
  	 *
  	 * @param {HTMLElement} domElement The DOM element to bind.
  	 * @param {module:engine/view/element~Element} viewElement The view element to bind.
  	 */
  	bindElements( domElement, viewElement ) {
  		this._domToViewMapping.set( domElement, viewElement );
  		this._viewToDomMapping.set( viewElement, domElement );
  	}
  
  	/**
  	 * Unbinds a given DOM element from the view element it was bound to. Unbinding is deep, meaning that all children of
  	 * the DOM element will be unbound too.
  	 *
  	 * @param {HTMLElement} domElement The DOM element to unbind.
  	 */
  	unbindDomElement( domElement ) {
  		const viewElement = this._domToViewMapping.get( domElement );
  
  		if ( viewElement ) {
  			this._domToViewMapping.delete( domElement );
  			this._viewToDomMapping.delete( viewElement );
  
  			for ( const child of domElement.childNodes ) {
  				this.unbindDomElement( child );
  			}
  		}
  	}
  
  	/**
  	 * Binds DOM and view document fragments, so it will be possible to get corresponding document fragments using
  	 * {@link module:engine/view/domconverter~DomConverter#mapDomToView} and
  	 * {@link module:engine/view/domconverter~DomConverter#mapViewToDom}.
  	 *
  	 * @param {DocumentFragment} domFragment The DOM document fragment to bind.
  	 * @param {module:engine/view/documentfragment~DocumentFragment} viewFragment The view document fragment to bind.
  	 */
  	bindDocumentFragments( domFragment, viewFragment ) {
  		this._domToViewMapping.set( domFragment, viewFragment );
  		this._viewToDomMapping.set( viewFragment, domFragment );
  	}
  
  	/**
  	 * Decides whether a given pair of attribute key and value should be passed further down the pipeline.
  	 *
  	 * @param {String} attributeKey
  	 * @param {String} attributeValue
  	 * @param {String} elementName Element name in lower case.
  	 * @returns {Boolean}
  	 */
  	shouldRenderAttribute( attributeKey, attributeValue, elementName ) {
  		if ( this.renderingMode === 'data' ) {
  			return true;
  		}
  
  		attributeKey = attributeKey.toLowerCase();
  
  		if ( attributeKey.startsWith( 'on' ) ) {
  			return false;
  		}
  
  		if (
  			attributeKey === 'srcdoc' &&
  			attributeValue.match( /\bon\S+\s*=|javascript:|<\s*\/*script/i )
  		) {
  			return false;
  		}
  
  		if (
  			elementName === 'img' &&
  			( attributeKey === 'src' || attributeKey === 'srcset' )
  		) {
  			return true;
  		}
  
  		if ( elementName === 'source' && attributeKey === 'srcset' ) {
  			return true;
  		}
  
  		if ( attributeValue.match( /^\s*(javascript:|data:(image\/svg|text\/x?html))/i ) ) {
  			return false;
  		}
  
  		return true;
  	}
  
  	/**
  	 * Set `domElement`'s content using provided `html` argument. Apply necessary filtering for the editing pipeline.
  	 *
  	 * @param {Element} domElement DOM element that should have `html` set as its content.
  	 * @param {String} html Textual representation of the HTML that will be set on `domElement`.
  	 */
  	setContentOf( domElement, html ) {
  		// For data pipeline we pass the HTML as-is.
  		if ( this.renderingMode === 'data' ) {
  			domElement.innerHTML = html;
  
  			return;
  		}
  
  		const document = new DOMParser().parseFromString( html, 'text/html' );
  		const fragment = document.createDocumentFragment();
  		const bodyChildNodes = document.body.childNodes;
  
  		while ( bodyChildNodes.length > 0 ) {
  			fragment.appendChild( bodyChildNodes[ 0 ] );
  		}
  
  		const treeWalker = document.createTreeWalker( fragment, NodeFilter.SHOW_ELEMENT );
  		const nodes = [];
  
  		let currentNode;
  
  		// eslint-disable-next-line no-cond-assign
  		while ( currentNode = treeWalker.nextNode() ) {
  			nodes.push( currentNode );
  		}
  
  		for ( const currentNode of nodes ) {
  			// Go through nodes to remove those that are prohibited in editing pipeline.
  			for ( const attributeName of currentNode.getAttributeNames() ) {
  				this.setDomElementAttribute( currentNode, attributeName, currentNode.getAttribute( attributeName ) );
  			}
  
  			const elementName = currentNode.tagName.toLowerCase();
  
  			// There are certain nodes, that should be renamed to <span> in editing pipeline.
  			if ( this._shouldRenameElement( elementName ) ) {
  				logWarning( 'domconverter-unsafe-element-detected', { unsafeElement: currentNode } );
  
  				currentNode.replaceWith( this._createReplacementDomElement( elementName, currentNode ) );
  			}
  		}
  
  		// Empty the target element.
  		while ( domElement.firstChild ) {
  			domElement.firstChild.remove();
  		}
  
  		domElement.append( fragment );
  	}
  
  	/**
  	 * Converts the view to the DOM. For all text nodes, not bound elements and document fragments new items will
  	 * be created. For bound elements and document fragments the method will return corresponding items.
  	 *
  	 * @param {module:engine/view/node~Node|module:engine/view/documentfragment~DocumentFragment} viewNode
  	 * View node or document fragment to transform.
  	 * @param {Document} domDocument Document which will be used to create DOM nodes.
  	 * @param {Object} [options] Conversion options.
  	 * @param {Boolean} [options.bind=false] Determines whether new elements will be bound.
  	 * @param {Boolean} [options.withChildren=true] If `true`, node's and document fragment's children will be converted too.
  	 * @returns {Node|DocumentFragment} Converted node or DocumentFragment.
  	 */
  	viewToDom( viewNode, domDocument, options = {} ) {
  		if ( viewNode.is( '$text' ) ) {
  			const textData = this._processDataFromViewText( viewNode );
  
  			return domDocument.createTextNode( textData );
  		} else {
  			if ( this.mapViewToDom( viewNode ) ) {
  				return this.mapViewToDom( viewNode );
  			}
  
  			let domElement;
  
  			if ( viewNode.is( 'documentFragment' ) ) {
  				// Create DOM document fragment.
  				domElement = domDocument.createDocumentFragment();
  
  				if ( options.bind ) {
  					this.bindDocumentFragments( domElement, viewNode );
  				}
  			} else if ( viewNode.is( 'uiElement' ) ) {
  				if ( viewNode.name === '$comment' ) {
  					domElement = domDocument.createComment( viewNode.getCustomProperty( '$rawContent' ) );
  				} else {
  					// UIElement has its own render() method (see #799).
  					domElement = viewNode.render( domDocument, this );
  				}
  
  				if ( options.bind ) {
  					this.bindElements( domElement, viewNode );
  				}
  
  				return domElement;
  			} else {
  				// Create DOM element.
  				if ( this._shouldRenameElement( viewNode.name ) ) {
  					logWarning( 'domconverter-unsafe-element-detected', { unsafeElement: viewNode } );
  
  					domElement = this._createReplacementDomElement( viewNode.name );
  				} else if ( viewNode.hasAttribute( 'xmlns' ) ) {
  					domElement = domDocument.createElementNS( viewNode.getAttribute( 'xmlns' ), viewNode.name );
  				} else {
  					domElement = domDocument.createElement( viewNode.name );
  				}
  
  				// RawElement take care of their children in RawElement#render() method which can be customized
  				// (see https://github.com/ckeditor/ckeditor5/issues/4469).
  				if ( viewNode.is( 'rawElement' ) ) {
  					viewNode.render( domElement, this );
  				}
  
  				if ( options.bind ) {
  					this.bindElements( domElement, viewNode );
  				}
  
  				// Copy element's attributes.
  				for ( const key of viewNode.getAttributeKeys() ) {
  					this.setDomElementAttribute( domElement, key, viewNode.getAttribute( key ), viewNode );
  				}
  			}
  
  			if ( options.withChildren !== false ) {
  				for ( const child of this.viewChildrenToDom( viewNode, domDocument, options ) ) {
  					domElement.appendChild( child );
  				}
  			}
  
  			return domElement;
  		}
  	}
  
  	/**
  	 * Sets the attribute on a DOM element.
  	 *
  	 * **Note**: To remove the attribute, use {@link #removeDomElementAttribute}.
  	 *
  	 * @param {HTMLElement} domElement The DOM element the attribute should be set on.
  	 * @param {String} key The name of the attribute.
  	 * @param {String} value The value of the attribute.
  	 * @param {module:engine/view/element~Element} [relatedViewElement] The view element related to the `domElement` (if there is any).
  	 * It helps decide whether the attribute set is unsafe. For instance, view elements created via
  	 * {@link module:engine/view/downcastwriter~DowncastWriter} methods can allow certain attributes that would normally be filtered out.
  	 */
  	setDomElementAttribute( domElement, key, value, relatedViewElement = null ) {
  		const shouldRenderAttribute = this.shouldRenderAttribute( key, value, domElement.tagName.toLowerCase() ) ||
  			relatedViewElement && relatedViewElement.shouldRenderUnsafeAttribute( key );
  
  		if ( !shouldRenderAttribute ) {
  			logWarning( 'domconverter-unsafe-attribute-detected', { domElement, key, value } );
  		}
  
  		// The old value was safe but the new value is unsafe.
  		if ( domElement.hasAttribute( key ) && !shouldRenderAttribute ) {
  			domElement.removeAttribute( key );
  		}
  		// The old value was unsafe (but prefixed) but the new value will be safe (will be unprefixed).
  		else if ( domElement.hasAttribute( UNSAFE_ATTRIBUTE_NAME_PREFIX + key ) && shouldRenderAttribute ) {
  			domElement.removeAttribute( UNSAFE_ATTRIBUTE_NAME_PREFIX + key );
  		}
  
  		// If the attribute should not be rendered, rename it (instead of removing) to give developers some idea of what
  		// is going on (https://github.com/ckeditor/ckeditor5/issues/10801).
  		domElement.setAttribute( shouldRenderAttribute ? key : UNSAFE_ATTRIBUTE_NAME_PREFIX + key, value );
  	}
  
  	/**
  	 * Removes an attribute from a DOM element.
  	 *
  	 * **Note**: To set the attribute, use {@link #setDomElementAttribute}.
  	 *
  	 * @param {HTMLElement} domElement The DOM element the attribute should be removed from.
  	 * @param {String} key The name of the attribute.
  	 */
  	removeDomElementAttribute( domElement, key ) {
  		// See #_createReplacementDomElement() to learn what this is.
  		if ( key == UNSAFE_ELEMENT_REPLACEMENT_ATTRIBUTE ) {
  			return;
  		}
  
  		domElement.removeAttribute( key );
  
  		// See setDomElementAttribute() to learn what this is.
  		domElement.removeAttribute( UNSAFE_ATTRIBUTE_NAME_PREFIX + key );
  	}
  
  	/**
  	 * Converts children of the view element to DOM using the
  	 * {@link module:engine/view/domconverter~DomConverter#viewToDom} method.
  	 * Additionally, this method adds block {@link module:engine/view/filler filler} to the list of children, if needed.
  	 *
  	 * @param {module:engine/view/element~Element|module:engine/view/documentfragment~DocumentFragment} viewElement Parent view element.
  	 * @param {Document} domDocument Document which will be used to create DOM nodes.
  	 * @param {Object} options See {@link module:engine/view/domconverter~DomConverter#viewToDom} options parameter.
  	 * @returns {Iterable.<Node>} DOM nodes.
  	 */
  	* viewChildrenToDom( viewElement, domDocument, options = {} ) {
  		const fillerPositionOffset = viewElement.getFillerOffset && viewElement.getFillerOffset();
  		let offset = 0;
  
  		for ( const childView of viewElement.getChildren() ) {
  			if ( fillerPositionOffset === offset ) {
  				yield this._getBlockFiller( domDocument );
  			}
  
  			yield this.viewToDom( childView, domDocument, options );
  
  			offset++;
  		}
  
  		if ( fillerPositionOffset === offset ) {
  			yield this._getBlockFiller( domDocument );
  		}
  	}
  
  	/**
  	 * Converts view {@link module:engine/view/range~Range} to DOM range.
  	 * Inline and block {@link module:engine/view/filler fillers} are handled during the conversion.
  	 *
  	 * @param {module:engine/view/range~Range} viewRange View range.
  	 * @returns {Range} DOM range.
  	 */
  	viewRangeToDom( viewRange ) {
  		const domStart = this.viewPositionToDom( viewRange.start );
  		const domEnd = this.viewPositionToDom( viewRange.end );
  
  		const domRange = document.createRange();
  		domRange.setStart( domStart.parent, domStart.offset );
  		domRange.setEnd( domEnd.parent, domEnd.offset );
  
  		return domRange;
  	}
  
  	/**
  	 * Converts view {@link module:engine/view/position~Position} to DOM parent and offset.
  	 *
  	 * Inline and block {@link module:engine/view/filler fillers} are handled during the conversion.
  	 * If the converted position is directly before inline filler it is moved inside the filler.
  	 *
  	 * @param {module:engine/view/position~Position} viewPosition View position.
  	 * @returns {Object|null} position DOM position or `null` if view position could not be converted to DOM.
  	 * @returns {Node} position.parent DOM position parent.
  	 * @returns {Number} position.offset DOM position offset.
  	 */
  	viewPositionToDom( viewPosition ) {
  		const viewParent = viewPosition.parent;
  
  		if ( viewParent.is( '$text' ) ) {
  			const domParent = this.findCorrespondingDomText( viewParent );
  
  			if ( !domParent ) {
  				// Position is in a view text node that has not been rendered to DOM yet.
  				return null;
  			}
  
  			let offset = viewPosition.offset;
  
  			if ( startsWithFiller( domParent ) ) {
  				offset += INLINE_FILLER_LENGTH;
  			}
  
  			return { parent: domParent, offset };
  		} else {
  			// viewParent is instance of ViewElement.
  			let domParent, domBefore, domAfter;
  
  			if ( viewPosition.offset === 0 ) {
  				domParent = this.mapViewToDom( viewParent );
  
  				if ( !domParent ) {
  					// Position is in a view element that has not been rendered to DOM yet.
  					return null;
  				}
  
  				domAfter = domParent.childNodes[ 0 ];
  			} else {
  				const nodeBefore = viewPosition.nodeBefore;
  
  				domBefore = nodeBefore.is( '$text' ) ?
  					this.findCorrespondingDomText( nodeBefore ) :
  					this.mapViewToDom( viewPosition.nodeBefore );
  
  				if ( !domBefore ) {
  					// Position is after a view element that has not been rendered to DOM yet.
  					return null;
  				}
  
  				domParent = domBefore.parentNode;
  				domAfter = domBefore.nextSibling;
  			}
  
  			// If there is an inline filler at position return position inside the filler. We should never return
  			// the position before the inline filler.
  			if ( isText( domAfter ) && startsWithFiller( domAfter ) ) {
  				return { parent: domAfter, offset: INLINE_FILLER_LENGTH };
  			}
  
  			const offset = domBefore ? indexOf( domBefore ) + 1 : 0;
  
  			return { parent: domParent, offset };
  		}
  	}
  
  	/**
  	 * Converts DOM to view. For all text nodes, not bound elements and document fragments new items will
  	 * be created. For bound elements and document fragments function will return corresponding items. For
  	 * {@link module:engine/view/filler fillers} `null` will be returned.
  	 * For all DOM elements rendered by {@link module:engine/view/uielement~UIElement} that UIElement will be returned.
  	 *
  	 * @param {Node|DocumentFragment} domNode DOM node or document fragment to transform.
  	 * @param {Object} [options] Conversion options.
  	 * @param {Boolean} [options.bind=false] Determines whether new elements will be bound.
  	 * @param {Boolean} [options.withChildren=true] If `true`, node's and document fragment's children will be converted too.
  	 * @param {Boolean} [options.keepOriginalCase=false] If `false`, node's tag name will be converted to lower case.
  	 * @param {Boolean} [options.skipComments=false] If `false`, comment nodes will be converted to `$comment`
  	 * {@link module:engine/view/uielement~UIElement view UI elements}.
  	 * @returns {module:engine/view/node~Node|module:engine/view/documentfragment~DocumentFragment|null} Converted node or document fragment
  	 * or `null` if DOM node is a {@link module:engine/view/filler filler} or the given node is an empty text node.
  	 */
  	domToView( domNode, options = {} ) {
  		if ( this.isBlockFiller( domNode ) ) {
  			return null;
  		}
  
  		// When node is inside a UIElement or a RawElement return that parent as it's view representation.
  		const hostElement = this.getHostViewElement( domNode );
  
  		if ( hostElement ) {
  			return hostElement;
  		}
  
  		if ( isComment( domNode ) && options.skipComments ) {
  			return null;
  		}
  
  		if ( isText( domNode ) ) {
  			if ( isInlineFiller( domNode ) ) {
  				return null;
  			} else {
  				const textData = this._processDataFromDomText( domNode );
  
  				return textData === '' ? null : new ViewText( this.document, textData );
  			}
  		} else {
  			if ( this.mapDomToView( domNode ) ) {
  				return this.mapDomToView( domNode );
  			}
  
  			let viewElement;
  
  			if ( this.isDocumentFragment( domNode ) ) {
  				// Create view document fragment.
  				viewElement = new ViewDocumentFragment( this.document );
  
  				if ( options.bind ) {
  					this.bindDocumentFragments( domNode, viewElement );
  				}
  			} else {
  				// Create view element.
  				viewElement = this._createViewElement( domNode, options );
  
  				if ( options.bind ) {
  					this.bindElements( domNode, viewElement );
  				}
  
  				// Copy element's attributes.
  				const attrs = domNode.attributes;
  
  				if ( attrs ) {
  					for ( let i = attrs.length - 1; i >= 0; i-- ) {
  						viewElement._setAttribute( attrs[ i ].name, attrs[ i ].value );
  					}
  				}
  
  				// Treat this element's content as a raw data if it was registered as such.
  				// Comment node is also treated as an element with raw data.
  				if ( this._isViewElementWithRawContent( viewElement, options ) || isComment( domNode ) ) {
  					const rawContent = isComment( domNode ) ? domNode.data : domNode.innerHTML;
  
  					viewElement._setCustomProperty( '$rawContent', rawContent );
  
  					// Store a DOM node to prevent left trimming of the following text node.
  					this._encounteredRawContentDomNodes.add( domNode );
  
  					return viewElement;
  				}
  			}
  
  			if ( options.withChildren !== false ) {
  				for ( const child of this.domChildrenToView( domNode, options ) ) {
  					viewElement._appendChild( child );
  				}
  			}
  
  			return viewElement;
  		}
  	}
  
  	/**
  	 * Converts children of the DOM element to view nodes using
  	 * the {@link module:engine/view/domconverter~DomConverter#domToView} method.
  	 * Additionally this method omits block {@link module:engine/view/filler filler}, if it exists in the DOM parent.
  	 *
  	 * @param {HTMLElement} domElement Parent DOM element.
  	 * @param {Object} options See {@link module:engine/view/domconverter~DomConverter#domToView} options parameter.
  	 * @returns {Iterable.<module:engine/view/node~Node>} View nodes.
  	 */
  	* domChildrenToView( domElement, options = {} ) {
  		for ( let i = 0; i < domElement.childNodes.length; i++ ) {
  			const domChild = domElement.childNodes[ i ];
  			const viewChild = this.domToView( domChild, options );
  
  			if ( viewChild !== null ) {
  				yield viewChild;
  			}
  		}
  	}
  
  	/**
  	 * Converts DOM selection to view {@link module:engine/view/selection~Selection}.
  	 * Ranges which cannot be converted will be omitted.
  	 *
  	 * @param {Selection} domSelection DOM selection.
  	 * @returns {module:engine/view/selection~Selection} View selection.
  	 */
  	domSelectionToView( domSelection ) {
  		// DOM selection might be placed in fake selection container.
  		// If container contains fake selection - return corresponding view selection.
  		if ( domSelection.rangeCount === 1 ) {
  			let container = domSelection.getRangeAt( 0 ).startContainer;
  
  			// The DOM selection might be moved to the text node inside the fake selection container.
  			if ( isText( container ) ) {
  				container = container.parentNode;
  			}
  
  			const viewSelection = this.fakeSelectionToView( container );
  
  			if ( viewSelection ) {
  				return viewSelection;
  			}
  		}
  
  		const isBackward = this.isDomSelectionBackward( domSelection );
  
  		const viewRanges = [];
  
  		for ( let i = 0; i < domSelection.rangeCount; i++ ) {
  			// DOM Range have correct start and end, no matter what is the DOM Selection direction. So we don't have to fix anything.
  			const domRange = domSelection.getRangeAt( i );
  			const viewRange = this.domRangeToView( domRange );
  
  			if ( viewRange ) {
  				viewRanges.push( viewRange );
  			}
  		}
  
  		return new ViewSelection( viewRanges, { backward: isBackward } );
  	}
  
  	/**
  	 * Converts DOM Range to view {@link module:engine/view/range~Range}.
  	 * If the start or end position can not be converted `null` is returned.
  	 *
  	 * @param {Range} domRange DOM range.
  	 * @returns {module:engine/view/range~Range|null} View range.
  	 */
  	domRangeToView( domRange ) {
  		const viewStart = this.domPositionToView( domRange.startContainer, domRange.startOffset );
  		const viewEnd = this.domPositionToView( domRange.endContainer, domRange.endOffset );
  
  		if ( viewStart && viewEnd ) {
  			return new ViewRange( viewStart, viewEnd );
  		}
  
  		return null;
  	}
  
  	/**
  	 * Converts DOM parent and offset to view {@link module:engine/view/position~Position}.
  	 *
  	 * If the position is inside a {@link module:engine/view/filler filler} which has no corresponding view node,
  	 * position of the filler will be converted and returned.
  	 *
  	 * If the position is inside DOM element rendered by {@link module:engine/view/uielement~UIElement}
  	 * that position will be converted to view position before that UIElement.
  	 *
  	 * If structures are too different and it is not possible to find corresponding position then `null` will be returned.
  	 *
  	 * @param {Node} domParent DOM position parent.
  	 * @param {Number} [domOffset=0] DOM position offset. You can skip it when converting the inline filler node.
  	 * @returns {module:engine/view/position~Position} viewPosition View position.
  	 */
  	domPositionToView( domParent, domOffset = 0 ) {
  		if ( this.isBlockFiller( domParent ) ) {
  			return this.domPositionToView( domParent.parentNode, indexOf( domParent ) );
  		}
  
  		// If position is somewhere inside UIElement or a RawElement - return position before that element.
  		const viewElement = this.mapDomToView( domParent );
  
  		if ( viewElement && ( viewElement.is( 'uiElement' ) || viewElement.is( 'rawElement' ) ) ) {
  			return ViewPosition._createBefore( viewElement );
  		}
  
  		if ( isText( domParent ) ) {
  			if ( isInlineFiller( domParent ) ) {
  				return this.domPositionToView( domParent.parentNode, indexOf( domParent ) );
  			}
  
  			const viewParent = this.findCorrespondingViewText( domParent );
  			let offset = domOffset;
  
  			if ( !viewParent ) {
  				return null;
  			}
  
  			if ( startsWithFiller( domParent ) ) {
  				offset -= INLINE_FILLER_LENGTH;
  				offset = offset < 0 ? 0 : offset;
  			}
  
  			return new ViewPosition( viewParent, offset );
  		}
  		// domParent instanceof HTMLElement.
  		else {
  			if ( domOffset === 0 ) {
  				const viewParent = this.mapDomToView( domParent );
  
  				if ( viewParent ) {
  					return new ViewPosition( viewParent, 0 );
  				}
  			} else {
  				const domBefore = domParent.childNodes[ domOffset - 1 ];
  				const viewBefore = isText( domBefore ) ?
  					this.findCorrespondingViewText( domBefore ) :
  					this.mapDomToView( domBefore );
  
  				// TODO #663
  				if ( viewBefore && viewBefore.parent ) {
  					return new ViewPosition( viewBefore.parent, viewBefore.index + 1 );
  				}
  			}
  
  			return null;
  		}
  	}
  
  	/**
  	 * Returns corresponding view {@link module:engine/view/element~Element Element} or
  	 * {@link module:engine/view/documentfragment~DocumentFragment} for provided DOM element or
  	 * document fragment. If there is no view item {@link module:engine/view/domconverter~DomConverter#bindElements bound}
  	 * to the given DOM - `undefined` is returned.
  	 *
  	 * For all DOM elements rendered by a {@link module:engine/view/uielement~UIElement} or
  	 * a {@link module:engine/view/rawelement~RawElement}, the parent `UIElement` or `RawElement` will be returned.
  	 *
  	 * @param {DocumentFragment|Element} domElementOrDocumentFragment DOM element or document fragment.
  	 * @returns {module:engine/view/element~Element|module:engine/view/documentfragment~DocumentFragment|undefined}
  	 * Corresponding view element, document fragment or `undefined` if no element was bound.
  	 */
  	mapDomToView( domElementOrDocumentFragment ) {
  		const hostElement = this.getHostViewElement( domElementOrDocumentFragment );
  
  		return hostElement || this._domToViewMapping.get( domElementOrDocumentFragment );
  	}
  
  	/**
  	 * Finds corresponding text node. Text nodes are not {@link module:engine/view/domconverter~DomConverter#bindElements bound},
  	 * corresponding text node is returned based on the sibling or parent.
  	 *
  	 * If the directly previous sibling is a {@link module:engine/view/domconverter~DomConverter#bindElements bound} element, it is used
  	 * to find the corresponding text node.
  	 *
  	 * If this is a first child in the parent and the parent is a {@link module:engine/view/domconverter~DomConverter#bindElements bound}
  	 * element, it is used to find the corresponding text node.
  	 *
  	 * For all text nodes rendered by a {@link module:engine/view/uielement~UIElement} or
  	 * a {@link module:engine/view/rawelement~RawElement}, the parent `UIElement` or `RawElement` will be returned.
  	 *
  	 * Otherwise `null` is returned.
  	 *
  	 * Note that for the block or inline {@link module:engine/view/filler filler} this method returns `null`.
  	 *
  	 * @param {Text} domText DOM text node.
  	 * @returns {module:engine/view/text~Text|null} Corresponding view text node or `null`, if it was not possible to find a
  	 * corresponding node.
  	 */
  	findCorrespondingViewText( domText ) {
  		if ( isInlineFiller( domText ) ) {
  			return null;
  		}
  
  		// If DOM text was rendered by a UIElement or a RawElement - return this parent element.
  		const hostElement = this.getHostViewElement( domText );
  
  		if ( hostElement ) {
  			return hostElement;
  		}
  
  		const previousSibling = domText.previousSibling;
  
  		// Try to use previous sibling to find the corresponding text node.
  		if ( previousSibling ) {
  			if ( !( this.isElement( previousSibling ) ) ) {
  				// The previous is text or comment.
  				return null;
  			}
  
  			const viewElement = this.mapDomToView( previousSibling );
  
  			if ( viewElement ) {
  				const nextSibling = viewElement.nextSibling;
  
  				// It might be filler which has no corresponding view node.
  				if ( nextSibling instanceof ViewText ) {
  					return viewElement.nextSibling;
  				} else {
  					return null;
  				}
  			}
  		}
  		// Try to use parent to find the corresponding text node.
  		else {
  			const viewElement = this.mapDomToView( domText.parentNode );
  
  			if ( viewElement ) {
  				const firstChild = viewElement.getChild( 0 );
  
  				// It might be filler which has no corresponding view node.
  				if ( firstChild instanceof ViewText ) {
  					return firstChild;
  				} else {
  					return null;
  				}
  			}
  		}
  
  		return null;
  	}
  
  	/**
  	 * Returns corresponding DOM item for provided {@link module:engine/view/element~Element Element} or
  	 * {@link module:engine/view/documentfragment~DocumentFragment DocumentFragment}.
  	 * To find a corresponding text for {@link module:engine/view/text~Text view Text instance}
  	 * use {@link #findCorrespondingDomText}.
  	 *
  	 * @param {module:engine/view/element~Element|module:engine/view/documentfragment~DocumentFragment} viewNode
  	 * View element or document fragment.
  	 * @returns {Node|DocumentFragment|undefined} Corresponding DOM node or document fragment.
  	 */
  	mapViewToDom( documentFragmentOrElement ) {
  		return this._viewToDomMapping.get( documentFragmentOrElement );
  	}
  
  	/**
  	 * Finds corresponding text node. Text nodes are not {@link module:engine/view/domconverter~DomConverter#bindElements bound},
  	 * corresponding text node is returned based on the sibling or parent.
  	 *
  	 * If the directly previous sibling is a {@link module:engine/view/domconverter~DomConverter#bindElements bound} element, it is used
  	 * to find the corresponding text node.
  	 *
  	 * If this is a first child in the parent and the parent is a {@link module:engine/view/domconverter~DomConverter#bindElements bound}
  	 * element, it is used to find the corresponding text node.
  	 *
  	 * Otherwise `null` is returned.
  	 *
  	 * @param {module:engine/view/text~Text} viewText View text node.
  	 * @returns {Text|null} Corresponding DOM text node or `null`, if it was not possible to find a corresponding node.
  	 */
  	findCorrespondingDomText( viewText ) {
  		const previousSibling = viewText.previousSibling;
  
  		// Try to use previous sibling to find the corresponding text node.
  		if ( previousSibling && this.mapViewToDom( previousSibling ) ) {
  			return this.mapViewToDom( previousSibling ).nextSibling;
  		}
  
  		// If this is a first node, try to use parent to find the corresponding text node.
  		if ( !previousSibling && viewText.parent && this.mapViewToDom( viewText.parent ) ) {
  			return this.mapViewToDom( viewText.parent ).childNodes[ 0 ];
  		}
  
  		return null;
  	}
  
  	/**
  	 * Focuses DOM editable that is corresponding to provided {@link module:engine/view/editableelement~EditableElement}.
  	 *
  	 * @param {module:engine/view/editableelement~EditableElement} viewEditable
  	 */
  	focus( viewEditable ) {
  		const domEditable = this.mapViewToDom( viewEditable );
  
  		if ( domEditable && domEditable.ownerDocument.activeElement !== domEditable ) {
  			// Save the scrollX and scrollY positions before the focus.
  			const { scrollX, scrollY } = global.window;
  			const scrollPositions = [];
  
  			// Save all scrollLeft and scrollTop values starting from domEditable up to
  			// document#documentElement.
  			forEachDomNodeAncestor( domEditable, node => {
  				const { scrollLeft, scrollTop } = node;
  
  				scrollPositions.push( [ scrollLeft, scrollTop ] );
  			} );
  
  			domEditable.focus();
  
  			// Restore scrollLeft and scrollTop values starting from domEditable up to
  			// document#documentElement.
  			// https://github.com/ckeditor/ckeditor5-engine/issues/951
  			// https://github.com/ckeditor/ckeditor5-engine/issues/957
  			forEachDomNodeAncestor( domEditable, node => {
  				const [ scrollLeft, scrollTop ] = scrollPositions.shift();
  
  				node.scrollLeft = scrollLeft;
  				node.scrollTop = scrollTop;
  			} );
  
  			// Restore the scrollX and scrollY positions after the focus.
  			// https://github.com/ckeditor/ckeditor5-engine/issues/951
  			global.window.scrollTo( scrollX, scrollY );
  		}
  	}
  
  	/**
  	 * Returns `true` when `node.nodeType` equals `Node.ELEMENT_NODE`.
  	 *
  	 * @param {Node} node Node to check.
  	 * @returns {Boolean}
  	 */
  	isElement( node ) {
  		return node && node.nodeType == Node.ELEMENT_NODE;
  	}
  
  	/**
  	 * Returns `true` when `node.nodeType` equals `Node.DOCUMENT_FRAGMENT_NODE`.
  	 *
  	 * @param {Node} node Node to check.
  	 * @returns {Boolean}
  	 */
  	isDocumentFragment( node ) {
  		return node && node.nodeType == Node.DOCUMENT_FRAGMENT_NODE;
  	}
  
  	/**
  	 * Checks if the node is an instance of the block filler for this DOM converter.
  	 *
  	 *		const converter = new DomConverter( viewDocument, { blockFillerMode: 'br' } );
  	 *
  	 *		converter.isBlockFiller( BR_FILLER( document ) ); // true
  	 *		converter.isBlockFiller( NBSP_FILLER( document ) ); // false
  	 *
  	 * **Note:**: For the `'nbsp'` mode the method also checks context of a node so it cannot be a detached node.
  	 *
  	 * **Note:** A special case in the `'nbsp'` mode exists where the `<br>` in `<p><br></p>` is treated as a block filler.
  	 *
  	 * @param {Node} domNode DOM node to check.
  	 * @returns {Boolean} True if a node is considered a block filler for given mode.
  	 */
  	isBlockFiller( domNode ) {
  		if ( this.blockFillerMode == 'br' ) {
  			return domNode.isEqualNode( BR_FILLER_REF );
  		}
  
  		// Special case for <p><br></p> in which <br> should be treated as filler even when we are not in the 'br' mode. See ckeditor5#5564.
  		if ( domNode.tagName === 'BR' && hasBlockParent( domNode, this.blockElements ) && domNode.parentNode.childNodes.length === 1 ) {
  			return true;
  		}
  
  		// If not in 'br' mode, try recognizing both marked and regular nbsp block fillers.
  		return domNode.isEqualNode( MARKED_NBSP_FILLER_REF ) || isNbspBlockFiller( domNode, this.blockElements );
  	}
  
  	/**
  	 * Returns `true` if given selection is a backward selection, that is, if it's `focus` is before `anchor`.
  	 *
  	 * @param {Selection} DOM Selection instance to check.
  	 * @returns {Boolean}
  	 */
  	isDomSelectionBackward( selection ) {
  		if ( selection.isCollapsed ) {
  			return false;
  		}
  
  		// Since it takes multiple lines of code to check whether a "DOM Position" is before/after another "DOM Position",
  		// we will use the fact that range will collapse if it's end is before it's start.
  		const range = document.createRange();
  
  		range.setStart( selection.anchorNode, selection.anchorOffset );
  		range.setEnd( selection.focusNode, selection.focusOffset );
  
  		const backward = range.collapsed;
  
  		range.detach();
  
  		return backward;
  	}
  
  	/**
  	 * Returns a parent {@link module:engine/view/uielement~UIElement} or {@link module:engine/view/rawelement~RawElement}
  	 * that hosts the provided DOM node. Returns `null` if there is no such parent.
  	 *
  	 * @param {Node} domNode
  	 * @returns {module:engine/view/uielement~UIElement|module:engine/view/rawelement~RawElement|null}
  	 */
  	getHostViewElement( domNode ) {
  		const ancestors = getAncestors( domNode );
  
  		// Remove domNode from the list.
  		ancestors.pop();
  
  		while ( ancestors.length ) {
  			const domNode = ancestors.pop();
  			const viewNode = this._domToViewMapping.get( domNode );
  
  			if ( viewNode && ( viewNode.is( 'uiElement' ) || viewNode.is( 'rawElement' ) ) ) {
  				return viewNode;
  			}
  		}
  
  		return null;
  	}
  
  	/**
  	 * Checks if the given selection's boundaries are at correct places.
  	 *
  	 * The following places are considered as incorrect for selection boundaries:
  	 *
  	 * * before or in the middle of an inline filler sequence,
  	 * * inside a DOM element which represents {@link module:engine/view/uielement~UIElement a view UI element},
  	 * * inside a DOM element which represents {@link module:engine/view/rawelement~RawElement a view raw element}.
  	 *
  	 * @param {Selection} domSelection The DOM selection object to be checked.
  	 * @returns {Boolean} `true` if the given selection is at a correct place, `false` otherwise.
  	 */
  	isDomSelectionCorrect( domSelection ) {
  		return this._isDomSelectionPositionCorrect( domSelection.anchorNode, domSelection.anchorOffset ) &&
  			this._isDomSelectionPositionCorrect( domSelection.focusNode, domSelection.focusOffset );
  	}
  
  	/**
  	 * Registers a {@link module:engine/view/matcher~MatcherPattern} for view elements whose content should be treated as raw data
  	 * and not processed during the conversion from DOM nodes to view elements.
  	 *
  	 * This is affecting how {@link module:engine/view/domconverter~DomConverter#domToView} and
  	 * {@link module:engine/view/domconverter~DomConverter#domChildrenToView} process DOM nodes.
  	 *
  	 * The raw data can be later accessed by a
  	 * {@link module:engine/view/element~Element#getCustomProperty custom property of a view element} called `"$rawContent"`.
  	 *
  	 * @param {module:engine/view/matcher~MatcherPattern} pattern Pattern matching a view element whose content should
  	 * be treated as raw data.
  	 */
  	registerRawContentMatcher( pattern ) {
  		this._rawContentElementMatcher.add( pattern );
  	}
  
  	/**
  	 * Returns the block {@link module:engine/view/filler filler} node based on the current {@link #blockFillerMode} setting.
  	 *
  	 * @private
  	 * @params {Document} domDocument
  	 * @returns {Node} filler
  	 */
  	_getBlockFiller( domDocument ) {
  		switch ( this.blockFillerMode ) {
  			case 'nbsp':
  				return NBSP_FILLER( domDocument ); // eslint-disable-line new-cap
  			case 'markedNbsp':
  				return MARKED_NBSP_FILLER( domDocument ); // eslint-disable-line new-cap
  			case 'br':
  				return BR_FILLER( domDocument ); // eslint-disable-line new-cap
  		}
  	}
  
  	/**
  	 * Checks if the given DOM position is a correct place for selection boundary. See {@link #isDomSelectionCorrect}.
  	 *
  	 * @private
  	 * @param {Element} domParent Position parent.
  	 * @param {Number} offset Position offset.
  	 * @returns {Boolean} `true` if given position is at a correct place for selection boundary, `false` otherwise.
  	 */
  	_isDomSelectionPositionCorrect( domParent, offset ) {
  		// If selection is before or in the middle of inline filler string, it is incorrect.
  		if ( isText( domParent ) && startsWithFiller( domParent ) && offset < INLINE_FILLER_LENGTH ) {
  			// Selection in a text node, at wrong position (before or in the middle of filler).
  			return false;
  		}
  
  		if ( this.isElement( domParent ) && startsWithFiller( domParent.childNodes[ offset ] ) ) {
  			// Selection in an element node, before filler text node.
  			return false;
  		}
  
  		const viewParent = this.mapDomToView( domParent );
  
  		// The position is incorrect when anchored inside a UIElement or a RawElement.
  		// Note: In case of UIElement and RawElement, mapDomToView() returns a parent element for any DOM child
  		// so there's no need to perform any additional checks.
  		if ( viewParent && ( viewParent.is( 'uiElement' ) || viewParent.is( 'rawElement' ) ) ) {
  			return false;
  		}
  
  		return true;
  	}
  
  	/**
  	 * Takes text data from a given {@link module:engine/view/text~Text#data} and processes it so
  	 * it is correctly displayed in the DOM.
  	 *
  	 * Following changes are done:
  	 *
  	 * * a space at the beginning is changed to `&nbsp;` if this is the first text node in its container
  	 * element or if a previous text node ends with a space character,
  	 * * space at the end of the text node is changed to `&nbsp;` if there are two spaces at the end of a node or if next node
  	 * starts with a space or if it is the last text node in its container,
  	 * * remaining spaces are replaced to a chain of spaces and `&nbsp;` (e.g. `'x   x'` becomes `'x &nbsp; x'`).
  	 *
  	 * Content of {@link #preElements} is not processed.
  	 *
  	 * @private
  	 * @param {module:engine/view/text~Text} node View text node to process.
  	 * @returns {String} Processed text data.
  	 */
  	_processDataFromViewText( node ) {
  		let data = node.data;
  
  		// If any of node ancestors has a name which is in `preElements` array, then currently processed
  		// view text node is (will be) in preformatted element. We should not change whitespaces then.
  		if ( node.getAncestors().some( parent => this.preElements.includes( parent.name ) ) ) {
  			return data;
  		}
  
  		// 1. Replace the first space with a nbsp if the previous node ends with a space or there is no previous node
  		// (container element boundary).
  		if ( data.charAt( 0 ) == ' ' ) {
  			const prevNode = this._getTouchingInlineViewNode( node, false );
  			const prevEndsWithSpace = prevNode && prevNode.is( '$textProxy' ) && this._nodeEndsWithSpace( prevNode );
  
  			if ( prevEndsWithSpace || !prevNode ) {
  				data = '\u00A0' + data.substr( 1 );
  			}
  		}
  
  		// 2. Replace the last space with nbsp if there are two spaces at the end or if the next node starts with space or there is no
  		// next node (container element boundary).
  		//
  		// Keep in mind that Firefox prefers $nbsp; before tag, not inside it:
  		//
  		// Foo <span>&nbsp;bar</span>  <-- bad.
  		// Foo&nbsp;<span> bar</span>  <-- good.
  		//
  		// More here: https://github.com/ckeditor/ckeditor5-engine/issues/1747.
  		if ( data.charAt( data.length - 1 ) == ' ' ) {
  			const nextNode = this._getTouchingInlineViewNode( node, true );
  			const nextStartsWithSpace = nextNode && nextNode.is( '$textProxy' ) && nextNode.data.charAt( 0 ) == ' ';
  
  			if ( data.charAt( data.length - 2 ) == ' ' || !nextNode || nextStartsWithSpace ) {
  				data = data.substr( 0, data.length - 1 ) + '\u00A0';
  			}
  		}
  
  		// 3. Create space+nbsp pairs.
  		return data.replace( / {2}/g, ' \u00A0' );
  	}
  
  	/**
  	 * Checks whether given node ends with a space character after changing appropriate space characters to `&nbsp;`s.
  	 *
  	 * @private
  	 * @param {module:engine/view/text~Text} node Node to check.
  	 * @returns {Boolean} `true` if given `node` ends with space, `false` otherwise.
  	 */
  	_nodeEndsWithSpace( node ) {
  		if ( node.getAncestors().some( parent => this.preElements.includes( parent.name ) ) ) {
  			return false;
  		}
  
  		const data = this._processDataFromViewText( node );
  
  		return data.charAt( data.length - 1 ) == ' ';
  	}
  
  	/**
  	 * Takes text data from native `Text` node and processes it to a correct {@link module:engine/view/text~Text view text node} data.
  	 *
  	 * Following changes are done:
  	 *
  	 * * multiple whitespaces are replaced to a single space,
  	 * * space at the beginning of a text node is removed if it is the first text node in its container
  	 * element or if the previous text node ends with a space character,
  	 * * space at the end of the text node is removed if there are two spaces at the end of a node or if next node
  	 * starts with a space or if it is the last text node in its container
  	 * * nbsps are converted to spaces.
  	 *
  	 * @param {Node} node DOM text node to process.
  	 * @returns {String} Processed data.
  	 * @private
  	 */
  	_processDataFromDomText( node ) {
  		let data = node.data;
  
  		if ( _hasDomParentOfType( node, this.preElements ) ) {
  			return getDataWithoutFiller( node );
  		}
  
  		// Change all consecutive whitespace characters (from the [ \n\t\r] set –
  		// see https://github.com/ckeditor/ckeditor5-engine/issues/822#issuecomment-311670249) to a single space character.
  		// That's how multiple whitespaces are treated when rendered, so we normalize those whitespaces.
  		// We're replacing 1+ (and not 2+) to also normalize singular \n\t\r characters (#822).
  		data = data.replace( /[ \n\t\r]{1,}/g, ' ' );
  
  		const prevNode = this._getTouchingInlineDomNode( node, false );
  		const nextNode = this._getTouchingInlineDomNode( node, true );
  
  		const shouldLeftTrim = this._checkShouldLeftTrimDomText( node, prevNode );
  		const shouldRightTrim = this._checkShouldRightTrimDomText( node, nextNode );
  
  		// If the previous dom text node does not exist or it ends by whitespace character, remove space character from the beginning
  		// of this text node. Such space character is treated as a whitespace.
  		if ( shouldLeftTrim ) {
  			data = data.replace( /^ /, '' );
  		}
  
  		// If the next text node does not exist remove space character from the end of this text node.
  		if ( shouldRightTrim ) {
  			data = data.replace( / $/, '' );
  		}
  
  		// At the beginning and end of a block element, Firefox inserts normal space + <br> instead of non-breaking space.
  		// This means that the text node starts/end with normal space instead of non-breaking space.
  		// This causes a problem because the normal space would be removed in `.replace` calls above. To prevent that,
  		// the inline filler is removed only after the data is initially processed (by the `.replace` above). See ckeditor5#692.
  		data = getDataWithoutFiller( new Text( data ) );
  
  		// At this point we should have removed all whitespaces from DOM text data.
  		//
  		// Now, We will reverse the process that happens in `_processDataFromViewText`.
  		//
  		// We have to change &nbsp; chars, that were in DOM text data because of rendering reasons, to spaces.
  		// First, change all ` \u00A0` pairs (space + &nbsp;) to two spaces. DOM converter changes two spaces from model/view to
  		// ` \u00A0` to ensure proper rendering. Since here we convert back, we recognize those pairs and change them back to `  `.
  		data = data.replace( / \u00A0/g, '  ' );
  
  		const isNextNodeInlineObjectElement = nextNode && this.isElement( nextNode ) && nextNode.tagName != 'BR';
  		const isNextNodeStartingWithSpace = nextNode && isText( nextNode ) && nextNode.data.charAt( 0 ) == ' ';
  
  		// Then, let's change the last nbsp to a space.
  		if ( /( |\u00A0)\u00A0$/.test( data ) || !nextNode || isNextNodeInlineObjectElement || isNextNodeStartingWithSpace ) {
  			data = data.replace( /\u00A0$/, ' ' );
  		}
  
  		// Then, change &nbsp; character that is at the beginning of the text node to space character.
  		// We do that replacement only if this is the first node or the previous node ends on whitespace character.
  		if ( shouldLeftTrim || prevNode && this.isElement( prevNode ) && prevNode.tagName != 'BR' ) {
  			data = data.replace( /^\u00A0/, ' ' );
  		}
  
  		// At this point, all whitespaces should be removed and all &nbsp; created for rendering reasons should be
  		// changed to normal space. All left &nbsp; are &nbsp; inserted intentionally.
  		return data;
  	}
  
  	/**
  	 * Helper function which checks if a DOM text node, preceded by the given `prevNode` should
  	 * be trimmed from the left side.
  	 *
  	 * @private
  	 * @param {Node} node
  	 * @param {Node} prevNode Either DOM text or `<br>` or one of `#inlineObjectElements`.
  	 */
  	_checkShouldLeftTrimDomText( node, prevNode ) {
  		if ( !prevNode ) {
  			return true;
  		}
  
  		if ( this.isElement( prevNode ) ) {
  			return prevNode.tagName === 'BR';
  		}
  
  		// Shouldn't left trim if previous node is a node that was encountered as a raw content node.
  		if ( this._encounteredRawContentDomNodes.has( node.previousSibling ) ) {
  			return false;
  		}
  
  		return /[^\S\u00A0]/.test( prevNode.data.charAt( prevNode.data.length - 1 ) );
  	}
  
  	/**
  	 * Helper function which checks if a DOM text node, succeeded by the given `nextNode` should
  	 * be trimmed from the right side.
  	 *
  	 * @private
  	 * @param {Node} node
  	 * @param {Node} nextNode Either DOM text or `<br>` or one of `#inlineObjectElements`.
  	 */
  	_checkShouldRightTrimDomText( node, nextNode ) {
  		if ( nextNode ) {
  			return false;
  		}
  
  		return !startsWithFiller( node );
  	}
  
  	/**
  	 * Helper function. For given {@link module:engine/view/text~Text view text node}, it finds previous or next sibling
  	 * that is contained in the same container element. If there is no such sibling, `null` is returned.
  	 *
  	 * @private
  	 * @param {module:engine/view/text~Text} node Reference node.
  	 * @param {Boolean} getNext
  	 * @returns {module:engine/view/text~Text|module:engine/view/element~Element|null} Touching text node, an inline object
  	 * or `null` if there is no next or previous touching text node.
  	 */
  	_getTouchingInlineViewNode( node, getNext ) {
  		const treeWalker = new ViewTreeWalker( {
  			startPosition: getNext ? ViewPosition._createAfter( node ) : ViewPosition._createBefore( node ),
  			direction: getNext ? 'forward' : 'backward'
  		} );
  
  		for ( const value of treeWalker ) {
  			// Found an inline object (for example an image).
  			if ( value.item.is( 'element' ) && this.inlineObjectElements.includes( value.item.name ) ) {
  				return value.item;
  			}
  			// ViewContainerElement is found on a way to next ViewText node, so given `node` was first/last
  			// text node in its container element.
  			else if ( value.item.is( 'containerElement' ) ) {
  				return null;
  			}
  			// <br> found – it works like a block boundary, so do not scan further.
  			else if ( value.item.is( 'element', 'br' ) ) {
  				return null;
  			}
  			// Found a text node in the same container element.
  			else if ( value.item.is( '$textProxy' ) ) {
  				return value.item;
  			}
  		}
  
  		return null;
  	}
  
  	/**
  	 * Helper function. For the given text node, it finds the closest touching node which is either
  	 * a text, `<br>` or an {@link #inlineObjectElements inline object}.
  	 *
  	 * If no such node is found, `null` is returned.
  	 *
  	 * For instance, in the following DOM structure:
  	 *
  	 *		<p>foo<b>bar</b><br>bom</p>
  	 *
  	 * * `foo` doesn't have its previous touching inline node (`null` is returned),
  	 * * `foo`'s next touching inline node is `bar`
  	 * * `bar`'s next touching inline node is `<br>`
  	 *
  	 * This method returns text nodes and `<br>` elements because these types of nodes affect how
  	 * spaces in the given text node need to be converted.
  	 *
  	 * @private
  	 * @param {Text} node
  	 * @param {Boolean} getNext
  	 * @returns {Text|Element|null}
  	 */
  	_getTouchingInlineDomNode( node, getNext ) {
  		if ( !node.parentNode ) {
  			return null;
  		}
  
  		const stepInto = getNext ? 'firstChild' : 'lastChild';
  		const stepOver = getNext ? 'nextSibling' : 'previousSibling';
  
  		let skipChildren = true;
  
  		do {
  			if ( !skipChildren && node[ stepInto ] ) {
  				node = node[ stepInto ];
  			} else if ( node[ stepOver ] ) {
  				node = node[ stepOver ];
  				skipChildren = false;
  			} else {
  				node = node.parentNode;
  				skipChildren = true;
  			}
  
  			if ( !node || this._isBlockElement( node ) ) {
  				return null;
  			}
  		} while (
  			!( isText( node ) || node.tagName == 'BR' || this._isInlineObjectElement( node ) )
  		);
  
  		return node;
  	}
  
  	/**
  	 * Returns `true` if a DOM node belongs to {@link #blockElements}. `false` otherwise.
  	 *
  	 * @private
  	 * @param {Node} node
  	 * @returns {Boolean}
  	 */
  	_isBlockElement( node ) {
  		return this.isElement( node ) && this.blockElements.includes( node.tagName.toLowerCase() );
  	}
  
  	/**
  	 * Returns `true` if a DOM node belongs to {@link #inlineObjectElements}. `false` otherwise.
  	 *
  	 * @private
  	 * @param {Node} node
  	 * @returns {Boolean}
  	 */
  	_isInlineObjectElement( node ) {
  		return this.isElement( node ) && this.inlineObjectElements.includes( node.tagName.toLowerCase() );
  	}
  
  	/**
  	 * Creates view element basing on the node type.
  	 *
  	 * @private
  	 * @param {Node} node DOM node to check.
  	 * @param {Object} options Conversion options. See {@link module:engine/view/domconverter~DomConverter#domToView} options parameter.
  	 * @returns {Element}
  	 */
  	_createViewElement( node, options ) {
  		if ( isComment( node ) ) {
  			return new ViewUIElement( this.document, '$comment' );
  		}
  
  		const viewName = options.keepOriginalCase ? node.tagName : node.tagName.toLowerCase();
  
  		return new ViewElement( this.document, viewName );
  	}
  
  	/**
  	 * Checks if view element's content should be treated as a raw data.
  	 *
  	 * @private
  	 * @param {Element} viewElement View element to check.
  	 * @param {Object} options Conversion options. See {@link module:engine/view/domconverter~DomConverter#domToView} options parameter.
  	 * @returns {Boolean}
  	 */
  	_isViewElementWithRawContent( viewElement, options ) {
  		return options.withChildren !== false && this._rawContentElementMatcher.match( viewElement );
  	}
  
  	/**
  	 * Checks whether a given element name should be renamed in a current rendering mode.
  	 *
  	 * @private
  	 * @param {String} elementName The name of view element.
  	 * @returns {Boolean}
  	 */
  	_shouldRenameElement( elementName ) {
  		return this.renderingMode == 'editing' && elementName.toLowerCase() == 'script';
  	}
  
  	/**
  	 * Return a <span> element with a special attribute holding the name of the original element.
  	 * Optionally, copy all the attributes of the original element if that element is provided.
  	 *
  	 * @private
  	 * @param {String} elementName The name of view element.
  	 * @param {Element} [originalDomElement] The original DOM element to copy attributes and content from.
  	 * @returns {Element}
  	 */
  	_createReplacementDomElement( elementName, originalDomElement = null ) {
  		const newDomElement = document.createElement( 'span' );
  
  		// Mark the span replacing a script as hidden.
  		newDomElement.setAttribute( UNSAFE_ELEMENT_REPLACEMENT_ATTRIBUTE, elementName );
  
  		if ( originalDomElement ) {
  			while ( originalDomElement.firstChild ) {
  				newDomElement.appendChild( originalDomElement.firstChild );
  			}
  
  			for ( const attributeName of originalDomElement.getAttributeNames() ) {
  				newDomElement.setAttribute( attributeName, originalDomElement.getAttribute( attributeName ) );
  			}
  		}
  
  		return newDomElement;
  	}
  }
  
  // Helper function.
  // Used to check if given native `Element` or `Text` node has parent with tag name from `types` array.
  //
  // @param {Node} node
  // @param {Array.<String>} types
  // @returns {Boolean} `true` if such parent exists or `false` if it does not.
  function _hasDomParentOfType( node, types ) {
  	const parents = getAncestors( node );
  
  	return parents.some( parent => parent.tagName && types.includes( parent.tagName.toLowerCase() ) );
  }
  
  // A helper that executes given callback for each DOM node's ancestor, starting from the given node
  // and ending in document#documentElement.
  //
  // @param {Node} node
  // @param {Function} callback A callback to be executed for each ancestor.
  function forEachDomNodeAncestor( node, callback ) {
  	while ( node && node != global.document ) {
  		callback( node );
  		node = node.parentNode;
  	}
  }
  
  // Checks if given node is a nbsp block filler.
  //
  // A &nbsp; is a block filler only if it is a single child of a block element.
  //
  // @param {Node} domNode DOM node.
  // @param {Array.<String>} blockElements
  // @returns {Boolean}
  function isNbspBlockFiller( domNode, blockElements ) {
  	const isNBSP = domNode.isEqualNode( NBSP_FILLER_REF );
  
  	return isNBSP && hasBlockParent( domNode, blockElements ) && domNode.parentNode.childNodes.length === 1;
  }
  
  // Checks if domNode has block parent.
  //
  // @param {Node} domNode DOM node.
  // @param {Array.<String>} blockElements
  // @returns {Boolean}
  function hasBlockParent( domNode, blockElements ) {
  	const parent = domNode.parentNode;
  
  	return parent && parent.tagName && blockElements.includes( parent.tagName.toLowerCase() );
  }
  
  /**
   * Enum representing the type of the block filler.
   *
   * Possible values:
   *
   * * `br` &ndash; For the `<br data-cke-filler="true">` block filler used in the editing view.
   * * `nbsp` &ndash; For the `&nbsp;` block fillers used in the data.
   * * `markedNbsp` &ndash; For the `&nbsp;` block fillers wrapped in `<span>` elements: `<span data-cke-filler="true">&nbsp;</span>`
   * used in the data.
   *
   * @typedef {String} module:engine/view/filler~BlockFillerMode
   */
  
  /**
   * The {@link module:engine/view/domconverter~DomConverter} detected a `<script>` element that may disrupt the
   * {@glink framework/guides/architecture/editing-engine#editing-pipeline editing pipeline} of the editor. To avoid this,
   * the `<script>` element was renamed to `<span data-ck-unsafe-element="script"></span>`.
   *
   * @error domconverter-unsafe-element-detected
   * @param {module:engine/model/element~Element|HTMLElement} unsafeElement The editing view or DOM element
   * that was renamed.
   */
  
  /**
   * The {@link module:engine/view/domconverter~DomConverter} detected an interactive attribute in the
   * {@glink framework/guides/architecture/editing-engine#editing-pipeline editing pipeline}. For the best
   * editing experience, the attribute was renamed to `data-ck-unsafe-attribute-[original attribute name]`.
   *
   * If you are the author of the plugin that generated this attribute and you want it to be preserved
   * in the editing pipeline, you can configure this when creating the element
   * using {@link module:engine/view/downcastwriter~DowncastWriter} during the
   * {@glink framework/guides/architecture/editing-engine#conversion model–view conversion}. Methods such as
   * {@link module:engine/view/downcastwriter~DowncastWriter#createContainerElement},
   * {@link module:engine/view/downcastwriter~DowncastWriter#createAttributeElement}, or
   * {@link module:engine/view/downcastwriter~DowncastWriter#createEmptyElement}
   * accept an option that will disable filtering of specific attributes:
   *
   *		const paragraph = writer.createContainerElement( 'p',
   *			{
   *				class: 'clickable-paragraph',
   *				onclick: 'alert( "Paragraph clicked!" )'
   *			},
   *			{
   *				// Make sure the "onclick" attribute will pass through.
   *				renderUnsafeAttributes: [ 'onclick' ]
   *			}
   *		);
   *
   * @error domconverter-unsafe-attribute-detected
   * @param {HTMLElement} domElement The DOM element the attribute was set on.
   * @param {String} key The original name of the attribute
   * @param {String} value The value of the original attribute
   */
  