extensions/emmet/src/updateImageSize.ts/getPropertyDelimitor
function getPropertyDelimitor(editor: TextEditor, node: Property): string {
	let anchor;
	if (anchor = (node.previousSibling || node.parent.contentStartToken)) {
		return editor.document.getText().substring(anchor.end, node.start);
	} else if (anchor = (node.nextSibling || node.parent.contentEndToken)) {
		return editor.document.getText().substring(node.end, anchor.start);
	}

	return '';
}