validateLanguageOptions(languageOptions) {
		const frontmatterOption = languageOptions?.frontmatter;
		const validFrontmatterOptions = new Set([
			false,
			"yaml",
			"toml",
			"json",
		]);

		if (
			frontmatterOption !== undefined &&
			!validFrontmatterOptions.has(frontmatterOption)
		) {
			throw new Error(
				`Invalid language option value \`${frontmatterOption}\` for frontmatter.`,
			);
		}
	}
Validates the language options.
@param {MarkdownLanguageOptions} languageOptions The language options to validate.
@returns {void}
@throws {Error} When the language options are invalid.