src/vs/editor/standalone/common/monarch/monarchLexer.ts/MonarchTokenizer/_getNestedEmbeddedLanguageData
class MonarchTokenizer:	private _getNestedEmbeddedLanguageData(languageId: string): EmbeddedLanguageData {
		if (!this._languageService.isRegisteredLanguageId(languageId)) {
			return new EmbeddedLanguageData(languageId, NullState);
		}

		if (languageId !== this._languageId) {
			// Fire language loading event
			languages.TokenizationRegistry.getOrCreate(languageId);
			this._embeddedLanguages[languageId] = true;
		}

		const tokenizationSupport = languages.TokenizationRegistry.get(languageId);
		if (tokenizationSupport) {
			return new EmbeddedLanguageData(languageId, tokenizationSupport.getInitialState());
		}

		return new EmbeddedLanguageData(languageId, NullState);
	}