How to use the @ckeditor/ckeditor5-utils/src/dom/istext function in @ckeditor/ckeditor5-utils

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;
		}
	}

return false;
		}

		// Note, we can't check if selection's position equals position of the
		// this._inlineFiller node, because of #663. We may not be able to calculate
		// the filler's position in the view at this stage.
		// Instead, we check it the other way – whether selection is anchored in
		// that text node or next to it.

		// Possible options are:
		// "FILLER{}"
		// "FILLERadded-text{}"
		const selectionPosition = this.selection.getFirstPosition();
		const position = this.domConverter.viewPositionToDom( selectionPosition );

		if ( position && isText( position.parent ) && startsWithFiller( position.parent ) ) {
			return true;
		}

		return false;
	}

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 };
		}
	}

domPositionToView( domParent, domOffset ) {
		if ( this.isBlockFiller( domParent, this.blockFillerMode ) ) {
			return this.domPositionToView( domParent.parentNode, indexOf( domParent ) );
		}

		// If position is somewhere inside UIElement - return position before that element.
		const viewElement = this.mapDomToView( domParent );

		if ( viewElement && viewElement.is( 'uiElement' ) ) {
			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;
			}

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.

function addInlineFiller( domDocument, domParentOrArray, offset ) {
	const childNodes = domParentOrArray instanceof Array ? domParentOrArray : domParentOrArray.childNodes;
	const nodeAfterFiller = childNodes[ offset ];

	if ( isText( nodeAfterFiller ) ) {
		nodeAfterFiller.data = INLINE_FILLER + nodeAfterFiller.data;

		return nodeAfterFiller;
	} else {
		const fillerNode = domDocument.createTextNode( INLINE_FILLER );

		if ( Array.isArray( domParentOrArray ) ) {
			childNodes.splice( offset, 0, fillerNode );
		} else {
			insertAt( domParentOrArray, offset, fillerNode );
		}

		return fillerNode;
	}
}

function isNbspBlockFiller( domNode, blockElements ) {
	const isNBSP = isText( domNode ) && domNode.data == '\u00A0';

	return isNBSP && hasBlockParent( domNode, blockElements ) && domNode.parentNode.childNodes.length === 1;
}

function areSimilar( node1, node2 ) {
	return isNode( node1 ) && isNode( node2 ) &&
		!isText( node1 ) && !isText( node2 ) &&
		node1.tagName.toLowerCase() === node2.tagName.toLowerCase();
}