/**
 * OPC part name normalization and relationship target resolution.
 *
 * Part names use forward-slash absolute grammar (`/xl/workbook.xml`).
 * Relationship targets resolve relative to the source part URI
 * (ECMA-376-2 Relationships).
 *
 * @private
 */
/**
 * Normalize a ZIP entry name or part name to an absolute OPC part name.
 * - Backslashes → forward slashes
 * - Ensure leading `/`
 * - Collapse duplicate slashes
 * - Remove `.` segments; reject `..` escape above root
 */
export declare function normalizePartName(name: string): string;
/**
 * Case-insensitive compare of OPC part names (used for Override PartName).
 */
export declare function partNamesEqual(a: string, b: string): boolean;
/**
 * Extension (without dot) for Default content type matching, lower-cased.
 * Returns undefined when the part has no extension.
 */
export declare function partExtension(partName: string): string | undefined;
/**
 * ZIP entry name for an absolute OPC part name (strip leading `/`).
 */
export declare function partNameToZipName(partName: string): string;
/**
 * Absolute OPC name of the relationships part for `sourcePart`.
 * Package-level: `sourcePart` is `null` → `/_rels/.rels`.
 * Part-level: `/xl/workbook.xml` → `/xl/_rels/workbook.xml.rels`.
 */
export declare function relationshipsPartNameFor(sourcePart: string | null): string;
/**
 * Resolve a relationship Target URI against a source part.
 * External targets are returned as-is (not fetched).
 */
export declare function resolveRelationshipTarget(sourcePart: string | null, target: string, targetMode: 'Internal' | 'External' | undefined): string;