Zref

zref is a LaTeX package that provides an extensible system for creating and retrieving cross-reference information. Designed as a replacement and extension of the standard LaTeX label/ref mechanism, zref allows authors and package developers to define named properties for labels, store arbitrary data in the auxiliary file, and later retrieve or test those properties during document processing.

The package is modular: a core implementation supplies basic labeling commands and storage, while optional modules add functionality such as absolute page numbers, line or page anchors, and integration with other packages. Because zref stores key–value properties per label, it supports use cases that require more than a single reference token—for example, capturing page offsets, formatting hints, or runtime computations tied to positions in the document.

zref is commonly distributed via CTAN and included in major TeX distributions. It is compatible with other referencing packages and can be combined with hyperref and varioref, though some modules are specifically designed for interaction. The package is extensible for package authors, enabling custom property definitions and retrieval hooks.

Developed to give TeX users finer control over cross-referencing, zref is used in complex documents and class or package development when the built-in LaTeX mechanisms are insufficient for advanced labeling needs.