extensions/html-language-features/server/src/modes/embeddedSupport.ts/getAttributeLanguage
function getAttributeLanguage(attributeName: string): string | null {
	let match = attributeName.match(/^(style)$|^(on\w+)$/i);
	if (!match) {
		return null;
	}
	return match[1] ? 'css' : 'javascript';
}