extensions/emmet/src/updateImageSize.ts/getImageSrcCSS
function getImageSrcCSS(editor: TextEditor, node: Property | undefined, position: Position): string | undefined {
	if (!node) {
		return;
	}
	const urlToken = findUrlToken(editor, node, position);
	if (!urlToken) {
		return;
	}

	// A stylesheet token may contain either quoted ('string') or unquoted URL
	let urlValue = urlToken.item(0);
	if (urlValue && urlValue.type === 'string') {
		urlValue = urlValue.item(0);
	}

	return urlValue && urlValue.valueOf();
}