/**
 * Font injection utility for cm-vertical-writing.
 *
 * This module provides a function to dynamically inject the pre-rotated
 * STVerticalMincho font into the document via @font-face, so that
 * consumers of the library do not need to manually host or reference the font.
 *
 * The font file (STVerticalMincho.ttf) is shipped alongside this library
 * under dist/fonts/ and loaded via a URL relative to the installed package.
 */
/**
 * Injects the bundled STVerticalMincho font into the document as a \@font-face rule.
 *
 * Call this once in your application entry point alongside `installPatches()`.
 * After calling this, you can use `'STVerticalMincho'` as the `fontFamily`
 * option in `verticalWriting()`.
 *
 * For SSR (Next.js, etc.), this function safe-guards against 'document is not defined'.
 *
 * @param fontUrl - Optional custom URL for the font file. If not provided,
 *                  it attempts to resolve the URL relative to the library.
 *
 * @example
 * ```ts
 * import { injectFont, installPatches, verticalWriting } from '@uozumi/cm-vertical-writing';
 *
 * // Automatically resolve font path
 * injectFont();
 *
 * // OR: Provide a custom path (useful for Next.js /public or CDNs)
 * injectFont('/fonts/STVerticalMincho.ttf');
 *
 * installPatches();
 * ```
 */
export declare function injectFont(fontUrl?: string): void;
