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, env, self) => {
			const token = tokens[idx];
			if (token.map && token.map.length) {
				token.attrJoin('class', 'hljs');
			}

			if (original) {
				return original(tokens, idx, options, env, self);
			} else {
				return self.renderToken(tokens, idx, options);
			}
		};
	}