extensions/markdown-language-features/src/markdownEngine.ts/MarkdownEngine/addFencedRenderer
class MarkdownEngine:	private addFencedRenderer(md: MarkdownIt): void {
		const original = md.renderer.rules['fenced'];
		md.renderer.rules['fenced'] = (tokens: Token[], idx: number, options: any, env: any, self: any) => {
			const token = tokens[idx];
			if (token.map && token.map.length) {
				token.attrJoin('class', 'hljs');
			}

			return original(tokens, idx, options, env, self);
		};
	}